Why can t I use switch statement on a String

Question

Is this functionality going to be put into a later Java version   Can someone explain why I can t do this  as in  the technical way Java s switch statement works

User · Answer

James Curran succinctly says   Switches based on integers can be optimized to very efficent code  Switches based on other data type can only be compiled to a series of if   statements  For that reason C  amp  C   only allow switches on integer types  since it was pointless with other types    My opinion  and it s only that  is that as soon as you start switching on non-primitives you need to start thinking about  equals  versus       Firstly comparing two strings can be a fairly lengthy procedure  adding to the performance problems that are mentioned above  Secondly if there is switching on strings there will be demand for switching on strings ignoring case  switching on strings considering ignoring locale switching on strings based on regex     I would approve of a decision that saved a lot of time for the language developers at the cost of a small amount of time for programmers

User · Answer

Switches based on integers can be optimized to very efficent code   Switches based on other data type can only be compiled to a series of if   statements   For that reason C  amp  C   only allow switches on integer types  since it was pointless with other  types   The designers of C  decided that the style was important  even if there was no advantage   The designers of Java apparently thought like the designers of C

User · Answer

The following is a complete example based on JeeBee s post  using java enum s instead of using a custom method   Note that in Java SE 7 and later you can use a String object in the switch statement s expression instead   public class Main                   param args the command line arguments            public static void main String   args           String current   args 0         Days currentDay   Days valueOf current toUpperCase            switch  currentDay              case MONDAY            case TUESDAY            case WEDNESDAY                System out println  boring                  break            case THURSDAY                System out println  getting better              case FRIDAY            case SATURDAY            case SUNDAY                System out println  much better                  break                  public enum Days        MONDAY      TUESDAY      WEDNESDAY      THURSDAY      FRIDAY      SATURDAY      SUNDAY

User · Answer

Beside the above good arguments  I will add that lot of people today see switch as an obsolete remainder of procedural past of Java  back to C times    I don t fully share this opinion  I think switch can have its usefulness in some cases  at least because of its speed  and anyway it is better than some series of cascading numerical else if I saw in some code     But indeed  it is worth looking at the case where you need a switch  and see if it cannot be replaced by something more OO  For example enums in Java 1 5   perhaps HashTable or some other collection  sometime I regret we don t have  anonymous  functions as first class citizen  as in Lua     which doesn t have switch     or JavaScript  or even polymorphism

User · Answer

Switch statements with String cases have been implemented in Java SE 7  at least 16 years after they were first requested  A clear reason for the delay was not provided  but it likely had to do with performance   Implementation in JDK 7  The feature has now been implemented in javac with a  de-sugaring  process  a clean  high-level syntax using String constants in case declarations is expanded at compile-time into more complex code following a pattern  The resulting code uses JVM instructions that have always existed   A switch with String cases is translated into two switches during compilation  The first maps each string to a unique integer mdash its position in the original switch  This is done by first switching on the hash code of the label  The corresponding case is an if statement that tests string equality  if there are collisions on the hash  the test is a cascading if-else-if  The second switch mirrors that in the original source code  but substitutes the case labels with their corresponding positions  This two-step process makes it easy to preserve the flow control of the original switch   Switches in the JVM  For more technical depth on switch  you can refer to the JVM Specification  where the compilation of switch statements is described  In a nutshell  there are two different JVM instructions that can be used for a switch  depending on the sparsity of the constants used by the cases  Both depend on using integer constants for each case to execute efficiently    If the constants are dense  they are used as an index  after subtracting the lowest value  into a table of instruction pointers mdash the tableswitch instruction    If the constants are sparse  a binary search for the correct case is performed mdash the lookupswitch instruction    In de-sugaring a switch on String objects  both instructions are likely to be used  The lookupswitch is suitable for the first switch on hash codes to find the original position of the case  The resulting ordinal is a natural fit for a tableswitch   Both instructions require the integer constants assigned to each case to be sorted at compile time  At runtime  while the O 1  performance of tableswitch generally appears better than the O log n   performance of lookupswitch  it requires some analysis to determine whether the table is dense enough to justify the space ndash time tradeoff  Bill Venners wrote a great article that covers this in more detail  along with an under-the-hood look at other Java flow control instructions   Before JDK 7  Prior to JDK 7  enum could approximate a String-based switch  This uses the static valueOf method generated by the compiler on every enum type  For example   Pill p   Pill valueOf str   switch p      case RED   pop     break    case BLUE  push    break

User · Answer

If you have a place in your code where you can switch on a String  then it may be better to refactor the String to be an enumeration of the possible values  which you can switch on  Of course  you limit the potential values of Strings you can have to those in the enumeration  which may or may not be desired   Of course your enumeration could have an entry for  other   and a fromString String  method  then you could have  ValueEnum enumval   ValueEnum fromString myString   switch  enumval       case MILK  lap    break     case WATER  sip    break     case BEER  quaff    break     case OTHER      default  dance    break

User · Answer

Switches based on integers can be optimized to very efficent code   Switches based on other data type can only be compiled to a series of if   statements   For that reason C  amp  C   only allow switches on integer types  since it was pointless with other  types   The designers of C  decided that the style was important  even if there was no advantage   The designers of Java apparently thought like the designers of C

User · Answer

Switch statements with String cases have been implemented in Java SE 7  at least 16 years after they were first requested  A clear reason for the delay was not provided  but it likely had to do with performance   Implementation in JDK 7  The feature has now been implemented in javac with a  de-sugaring  process  a clean  high-level syntax using String constants in case declarations is expanded at compile-time into more complex code following a pattern  The resulting code uses JVM instructions that have always existed   A switch with String cases is translated into two switches during compilation  The first maps each string to a unique integer mdash its position in the original switch  This is done by first switching on the hash code of the label  The corresponding case is an if statement that tests string equality  if there are collisions on the hash  the test is a cascading if-else-if  The second switch mirrors that in the original source code  but substitutes the case labels with their corresponding positions  This two-step process makes it easy to preserve the flow control of the original switch   Switches in the JVM  For more technical depth on switch  you can refer to the JVM Specification  where the compilation of switch statements is described  In a nutshell  there are two different JVM instructions that can be used for a switch  depending on the sparsity of the constants used by the cases  Both depend on using integer constants for each case to execute efficiently    If the constants are dense  they are used as an index  after subtracting the lowest value  into a table of instruction pointers mdash the tableswitch instruction    If the constants are sparse  a binary search for the correct case is performed mdash the lookupswitch instruction    In de-sugaring a switch on String objects  both instructions are likely to be used  The lookupswitch is suitable for the first switch on hash codes to find the original position of the case  The resulting ordinal is a natural fit for a tableswitch   Both instructions require the integer constants assigned to each case to be sorted at compile time  At runtime  while the O 1  performance of tableswitch generally appears better than the O log n   performance of lookupswitch  it requires some analysis to determine whether the table is dense enough to justify the space ndash time tradeoff  Bill Venners wrote a great article that covers this in more detail  along with an under-the-hood look at other Java flow control instructions   Before JDK 7  Prior to JDK 7  enum could approximate a String-based switch  This uses the static valueOf method generated by the compiler on every enum type  For example   Pill p   Pill valueOf str   switch p      case RED   pop     break    case BLUE  push    break

User · Answer

In Java 11  it s possible with variables too  The only condition is it must be a constant  For Example  final String LEFT    quot left quot   final String RIGHT    quot right quot   final String UP    quot up quot   final String DOWN    quot down quot    String var         switch  var        case LEFT      case RIGHT      case DOWN      default          return 0     PS  I ve not tried this with earlier jdks  So please update the answer if it s supported there too

User · Answer

public class StringSwitchCase         public static void main String args               visitIsland  Santorini             visitIsland  Crete             visitIsland  Paros                  public static void visitIsland String island             switch island              case  Corfu                   System out println  User wants to visit Corfu                   break             case  Crete                   System out println  User wants to visit Crete                   break             case  Santorini                   System out println  User wants to visit Santorini                   break             case  Mykonos                   System out println  User wants to visit Mykonos                   break            default                  System out println  Unknown Island                   break

User · Answer

Not very pretty  but here is another way for Java 6 and bellow    String runFct            queryType equals  eq      method1           queryType equals  L L     method2           queryType equals  L R     method3           queryType equals  L LR     method4                method5   Method m   this getClass   getMethod runFct   m invoke this

User · Answer

Switch statements with String cases have been implemented in Java SE 7  at least 16 years after they were first requested  A clear reason for the delay was not provided  but it likely had to do with performance   Implementation in JDK 7  The feature has now been implemented in javac with a  de-sugaring  process  a clean  high-level syntax using String constants in case declarations is expanded at compile-time into more complex code following a pattern  The resulting code uses JVM instructions that have always existed   A switch with String cases is translated into two switches during compilation  The first maps each string to a unique integer mdash its position in the original switch  This is done by first switching on the hash code of the label  The corresponding case is an if statement that tests string equality  if there are collisions on the hash  the test is a cascading if-else-if  The second switch mirrors that in the original source code  but substitutes the case labels with their corresponding positions  This two-step process makes it easy to preserve the flow control of the original switch   Switches in the JVM  For more technical depth on switch  you can refer to the JVM Specification  where the compilation of switch statements is described  In a nutshell  there are two different JVM instructions that can be used for a switch  depending on the sparsity of the constants used by the cases  Both depend on using integer constants for each case to execute efficiently    If the constants are dense  they are used as an index  after subtracting the lowest value  into a table of instruction pointers mdash the tableswitch instruction    If the constants are sparse  a binary search for the correct case is performed mdash the lookupswitch instruction    In de-sugaring a switch on String objects  both instructions are likely to be used  The lookupswitch is suitable for the first switch on hash codes to find the original position of the case  The resulting ordinal is a natural fit for a tableswitch   Both instructions require the integer constants assigned to each case to be sorted at compile time  At runtime  while the O 1  performance of tableswitch generally appears better than the O log n   performance of lookupswitch  it requires some analysis to determine whether the table is dense enough to justify the space ndash time tradeoff  Bill Venners wrote a great article that covers this in more detail  along with an under-the-hood look at other Java flow control instructions   Before JDK 7  Prior to JDK 7  enum could approximate a String-based switch  This uses the static valueOf method generated by the compiler on every enum type  For example   Pill p   Pill valueOf str   switch p      case RED   pop     break    case BLUE  push    break

User · Answer

The following is a complete example based on JeeBee s post  using java enum s instead of using a custom method   Note that in Java SE 7 and later you can use a String object in the switch statement s expression instead   public class Main                   param args the command line arguments            public static void main String   args           String current   args 0         Days currentDay   Days valueOf current toUpperCase            switch  currentDay              case MONDAY            case TUESDAY            case WEDNESDAY                System out println  boring                  break            case THURSDAY                System out println  getting better              case FRIDAY            case SATURDAY            case SUNDAY                System out println  much better                  break                  public enum Days        MONDAY      TUESDAY      WEDNESDAY      THURSDAY      FRIDAY      SATURDAY      SUNDAY

User · Answer

Beside the above good arguments  I will add that lot of people today see switch as an obsolete remainder of procedural past of Java  back to C times    I don t fully share this opinion  I think switch can have its usefulness in some cases  at least because of its speed  and anyway it is better than some series of cascading numerical else if I saw in some code     But indeed  it is worth looking at the case where you need a switch  and see if it cannot be replaced by something more OO  For example enums in Java 1 5   perhaps HashTable or some other collection  sometime I regret we don t have  anonymous  functions as first class citizen  as in Lua     which doesn t have switch     or JavaScript  or even polymorphism

User · Answer

In Java 11  it s possible with variables too  The only condition is it must be a constant  For Example  final String LEFT    quot left quot   final String RIGHT    quot right quot   final String UP    quot up quot   final String DOWN    quot down quot    String var         switch  var        case LEFT      case RIGHT      case DOWN      default          return 0     PS  I ve not tried this with earlier jdks  So please update the answer if it s supported there too

User · Answer

Other answers have said this was added in Java 7 and given workarounds for earlier versions  This answer tries to answer the  why   Java was a reaction to the over-complexities of C    It was designed to be a simple clean language   String got a little bit of special case handling in the language but it seems clear to me that the designers were trying to keep the amount of special casing and syntactic sugar to a minimum   switching on strings is fairly complex under the hood since strings are not simple primitive types  It was not a common feature at the time Java was designed and doesn t really fit in well with the minimalist design  Especially as they had decided not to special case    for strings  it would be  and is  a bit strange for case to work where    doesn t   Between 1 0 and 1 4 the language itself stayed pretty much the same  Most of the enhancements to Java were on the library side    That all changed with Java 5  the language was substantially extended  Further extensions followed in versions 7 and 8  I expect that this change of attitude was driven by the rise of C

User · Answer

It s a breeze in Groovy  I embed the groovy jar and create a groovy utility class to do all these things and more which I find exasperating to do in Java  since I am stuck using Java 6 in the enterprise    it  p  each  switch  it  name text        case  choclate        myholder myval  it text          break

User · Answer

Switch statements with String cases have been implemented in Java SE 7  at least 16 years after they were first requested  A clear reason for the delay was not provided  but it likely had to do with performance   Implementation in JDK 7  The feature has now been implemented in javac with a  de-sugaring  process  a clean  high-level syntax using String constants in case declarations is expanded at compile-time into more complex code following a pattern  The resulting code uses JVM instructions that have always existed   A switch with String cases is translated into two switches during compilation  The first maps each string to a unique integer mdash its position in the original switch  This is done by first switching on the hash code of the label  The corresponding case is an if statement that tests string equality  if there are collisions on the hash  the test is a cascading if-else-if  The second switch mirrors that in the original source code  but substitutes the case labels with their corresponding positions  This two-step process makes it easy to preserve the flow control of the original switch   Switches in the JVM  For more technical depth on switch  you can refer to the JVM Specification  where the compilation of switch statements is described  In a nutshell  there are two different JVM instructions that can be used for a switch  depending on the sparsity of the constants used by the cases  Both depend on using integer constants for each case to execute efficiently    If the constants are dense  they are used as an index  after subtracting the lowest value  into a table of instruction pointers mdash the tableswitch instruction    If the constants are sparse  a binary search for the correct case is performed mdash the lookupswitch instruction    In de-sugaring a switch on String objects  both instructions are likely to be used  The lookupswitch is suitable for the first switch on hash codes to find the original position of the case  The resulting ordinal is a natural fit for a tableswitch   Both instructions require the integer constants assigned to each case to be sorted at compile time  At runtime  while the O 1  performance of tableswitch generally appears better than the O log n   performance of lookupswitch  it requires some analysis to determine whether the table is dense enough to justify the space ndash time tradeoff  Bill Venners wrote a great article that covers this in more detail  along with an under-the-hood look at other Java flow control instructions   Before JDK 7  Prior to JDK 7  enum could approximate a String-based switch  This uses the static valueOf method generated by the compiler on every enum type  For example   Pill p   Pill valueOf str   switch p      case RED   pop     break    case BLUE  push    break

User · Answer

James Curran succinctly says   Switches based on integers can be optimized to very efficent code  Switches based on other data type can only be compiled to a series of if   statements  For that reason C  amp  C   only allow switches on integer types  since it was pointless with other types    My opinion  and it s only that  is that as soon as you start switching on non-primitives you need to start thinking about  equals  versus       Firstly comparing two strings can be a fairly lengthy procedure  adding to the performance problems that are mentioned above  Secondly if there is switching on strings there will be demand for switching on strings ignoring case  switching on strings considering ignoring locale switching on strings based on regex     I would approve of a decision that saved a lot of time for the language developers at the cost of a small amount of time for programmers

User · Answer

For years we ve been using a n open source  preprocessor for this      switch target  case  foo   code     end   Preprocessed files are named Foo jpp and get processed into Foo java with an ant script   Advantage is it is processed into Java that runs on 1 0  although typically we only supported back to 1 4   Also it was far easier to do this  lots of string switches  compared to fudging it with enums or other workarounds - code was a lot easier to read  maintain  and understand  IIRC  can t provide statistics or technical reasoning at this point  it was also faster than the natural Java equivalents   Disadvantages are you aren t editing Java so it s a bit more workflow  edit  process  compile test  plus an IDE will link back to the Java which is a little convoluted  the switch becomes a series of if else logic steps  and the switch case order is not maintained   I wouldn t recommend it for 1 7  but it s useful if you want to program Java that targets earlier JVMs  since Joe public rarely has the latest installed    You can get it from SVN or browse the code online  You ll need EBuild to build it as-is

User · Answer

James Curran succinctly says   Switches based on integers can be optimized to very efficent code  Switches based on other data type can only be compiled to a series of if   statements  For that reason C  amp  C   only allow switches on integer types  since it was pointless with other types    My opinion  and it s only that  is that as soon as you start switching on non-primitives you need to start thinking about  equals  versus       Firstly comparing two strings can be a fairly lengthy procedure  adding to the performance problems that are mentioned above  Secondly if there is switching on strings there will be demand for switching on strings ignoring case  switching on strings considering ignoring locale switching on strings based on regex     I would approve of a decision that saved a lot of time for the language developers at the cost of a small amount of time for programmers

User · Answer

JEP 354  Switch Expressions  Preview  in JDK-13 and JEP 361  Switch Expressions  Standard  in JDK-14 will extend the switch statement so it can be used as an expression    Now you can    directly assign variable from switch expression   use new form of switch label  case L - gt        The code to the right of a  case L -   switch label is restricted to be an expression  a block  or  for convenience  a throw statement   use multiple constants per case  separated by commas   and also there are no more value breaks      To yield a value from a switch expression  the break with value statement is dropped in favor of a yield statement     So the demo from the answers  1  2  might look like this     public static void main String   args        switch  args 0           case  Monday    Tuesday    Wednesday  - gt   System out println  boring          case  Thursday  - gt  System out println  getting better          case  Friday    Saturday    Sunday  - gt  System out println  much better

User · Answer

If you are not using JDK7 or higher  you can use hashCode   to simulate it  Because String hashCode   usually returns different values for different strings and always returns equal values for equal strings  it is fairly reliable  Different strings can produce the same hash code as  Lii mentioned in a comment  such as  FB  and  Ea   See documentation   So  the code would look like this   String s     lt Your String gt     switch s hashCode      case  Hello  hashCode    break  case  Goodbye  hashCode    break      That way  you are technically switching on an int   Alternatively  you could use the following code   public final class Switch lt T gt        private final HashMap lt T  Runnable gt  cases   new HashMap lt T  Runnable gt  0        public void addCase T object  Runnable action            this cases put object  action              public void SWITCH T object            for  T t   this cases keySet                  if  object equals t        This means that the class works with any object                  this cases get t  run                    break

User · Answer

Beside the above good arguments  I will add that lot of people today see switch as an obsolete remainder of procedural past of Java  back to C times    I don t fully share this opinion  I think switch can have its usefulness in some cases  at least because of its speed  and anyway it is better than some series of cascading numerical else if I saw in some code     But indeed  it is worth looking at the case where you need a switch  and see if it cannot be replaced by something more OO  For example enums in Java 1 5   perhaps HashTable or some other collection  sometime I regret we don t have  anonymous  functions as first class citizen  as in Lua     which doesn t have switch     or JavaScript  or even polymorphism

User · Answer

When you use intellij also look at   File -  Project Structure -  Project  File -  Project Structure -  Modules  When you have multiple modules make sure you set the correct language level in the module tab

User · Answer

For years we ve been using a n open source  preprocessor for this      switch target  case  foo   code     end   Preprocessed files are named Foo jpp and get processed into Foo java with an ant script   Advantage is it is processed into Java that runs on 1 0  although typically we only supported back to 1 4   Also it was far easier to do this  lots of string switches  compared to fudging it with enums or other workarounds - code was a lot easier to read  maintain  and understand  IIRC  can t provide statistics or technical reasoning at this point  it was also faster than the natural Java equivalents   Disadvantages are you aren t editing Java so it s a bit more workflow  edit  process  compile test  plus an IDE will link back to the Java which is a little convoluted  the switch becomes a series of if else logic steps  and the switch case order is not maintained   I wouldn t recommend it for 1 7  but it s useful if you want to program Java that targets earlier JVMs  since Joe public rarely has the latest installed    You can get it from SVN or browse the code online  You ll need EBuild to build it as-is

User · Answer

Not very pretty  but here is another way for Java 6 and bellow    String runFct            queryType equals  eq      method1           queryType equals  L L     method2           queryType equals  L R     method3           queryType equals  L LR     method4                method5   Method m   this getClass   getMethod runFct   m invoke this

User · Answer

If you have a place in your code where you can switch on a String  then it may be better to refactor the String to be an enumeration of the possible values  which you can switch on  Of course  you limit the potential values of Strings you can have to those in the enumeration  which may or may not be desired   Of course your enumeration could have an entry for  other   and a fromString String  method  then you could have  ValueEnum enumval   ValueEnum fromString myString   switch  enumval       case MILK  lap    break     case WATER  sip    break     case BEER  quaff    break     case OTHER      default  dance    break

User · Answer

If you are not using JDK7 or higher  you can use hashCode   to simulate it  Because String hashCode   usually returns different values for different strings and always returns equal values for equal strings  it is fairly reliable  Different strings can produce the same hash code as  Lii mentioned in a comment  such as  FB  and  Ea   See documentation   So  the code would look like this   String s     lt Your String gt     switch s hashCode      case  Hello  hashCode    break  case  Goodbye  hashCode    break      That way  you are technically switching on an int   Alternatively  you could use the following code   public final class Switch lt T gt        private final HashMap lt T  Runnable gt  cases   new HashMap lt T  Runnable gt  0        public void addCase T object  Runnable action            this cases put object  action              public void SWITCH T object            for  T t   this cases keySet                  if  object equals t        This means that the class works with any object                  this cases get t  run                    break

User · Answer

It s a breeze in Groovy  I embed the groovy jar and create a groovy utility class to do all these things and more which I find exasperating to do in Java  since I am stuck using Java 6 in the enterprise    it  p  each  switch  it  name text        case  choclate        myholder myval  it text          break

User · Answer

An example of direct String usage since 1 7 may be shown as well   public static void main String   args         switch  args 0             case  Monday           case  Tuesday           case  Wednesday               System out println  boring                break          case  Thursday               System out println  getting better            case  Friday           case  Saturday           case  Sunday               System out println  much better                break

User · Answer

When you use intellij also look at   File -  Project Structure -  Project  File -  Project Structure -  Modules  When you have multiple modules make sure you set the correct language level in the module tab

User · Answer

Beside the above good arguments  I will add that lot of people today see switch as an obsolete remainder of procedural past of Java  back to C times    I don t fully share this opinion  I think switch can have its usefulness in some cases  at least because of its speed  and anyway it is better than some series of cascading numerical else if I saw in some code     But indeed  it is worth looking at the case where you need a switch  and see if it cannot be replaced by something more OO  For example enums in Java 1 5   perhaps HashTable or some other collection  sometime I regret we don t have  anonymous  functions as first class citizen  as in Lua     which doesn t have switch     or JavaScript  or even polymorphism

User · Answer

public class StringSwitchCase         public static void main String args               visitIsland  Santorini             visitIsland  Crete             visitIsland  Paros                  public static void visitIsland String island             switch island              case  Corfu                   System out println  User wants to visit Corfu                   break             case  Crete                   System out println  User wants to visit Crete                   break             case  Santorini                   System out println  User wants to visit Santorini                   break             case  Mykonos                   System out println  User wants to visit Mykonos                   break            default                  System out println  Unknown Island                   break

User · Answer

James Curran succinctly says   Switches based on integers can be optimized to very efficent code  Switches based on other data type can only be compiled to a series of if   statements  For that reason C  amp  C   only allow switches on integer types  since it was pointless with other types    My opinion  and it s only that  is that as soon as you start switching on non-primitives you need to start thinking about  equals  versus       Firstly comparing two strings can be a fairly lengthy procedure  adding to the performance problems that are mentioned above  Secondly if there is switching on strings there will be demand for switching on strings ignoring case  switching on strings considering ignoring locale switching on strings based on regex     I would approve of a decision that saved a lot of time for the language developers at the cost of a small amount of time for programmers

User · Answer

Switches based on integers can be optimized to very efficent code   Switches based on other data type can only be compiled to a series of if   statements   For that reason C  amp  C   only allow switches on integer types  since it was pointless with other  types   The designers of C  decided that the style was important  even if there was no advantage   The designers of Java apparently thought like the designers of C

User · Answer

If you have a place in your code where you can switch on a String  then it may be better to refactor the String to be an enumeration of the possible values  which you can switch on  Of course  you limit the potential values of Strings you can have to those in the enumeration  which may or may not be desired   Of course your enumeration could have an entry for  other   and a fromString String  method  then you could have  ValueEnum enumval   ValueEnum fromString myString   switch  enumval       case MILK  lap    break     case WATER  sip    break     case BEER  quaff    break     case OTHER      default  dance    break

User · Answer

An example of direct String usage since 1 7 may be shown as well   public static void main String   args         switch  args 0             case  Monday           case  Tuesday           case  Wednesday               System out println  boring                break          case  Thursday               System out println  getting better            case  Friday           case  Saturday           case  Sunday               System out println  much better                break

User · Answer

Other answers have said this was added in Java 7 and given workarounds for earlier versions  This answer tries to answer the  why   Java was a reaction to the over-complexities of C    It was designed to be a simple clean language   String got a little bit of special case handling in the language but it seems clear to me that the designers were trying to keep the amount of special casing and syntactic sugar to a minimum   switching on strings is fairly complex under the hood since strings are not simple primitive types  It was not a common feature at the time Java was designed and doesn t really fit in well with the minimalist design  Especially as they had decided not to special case    for strings  it would be  and is  a bit strange for case to work where    doesn t   Between 1 0 and 1 4 the language itself stayed pretty much the same  Most of the enhancements to Java were on the library side    That all changed with Java 5  the language was substantially extended  Further extensions followed in versions 7 and 8  I expect that this change of attitude was driven by the rise of C

User · Answer

Switches based on integers can be optimized to very efficent code   Switches based on other data type can only be compiled to a series of if   statements   For that reason C  amp  C   only allow switches on integer types  since it was pointless with other  types   The designers of C  decided that the style was important  even if there was no advantage   The designers of Java apparently thought like the designers of C

User · Answer

JEP 354  Switch Expressions  Preview  in JDK-13 and JEP 361  Switch Expressions  Standard  in JDK-14 will extend the switch statement so it can be used as an expression    Now you can    directly assign variable from switch expression   use new form of switch label  case L - gt        The code to the right of a  case L -   switch label is restricted to be an expression  a block  or  for convenience  a throw statement   use multiple constants per case  separated by commas   and also there are no more value breaks      To yield a value from a switch expression  the break with value statement is dropped in favor of a yield statement     So the demo from the answers  1  2  might look like this     public static void main String   args        switch  args 0           case  Monday    Tuesday    Wednesday  - gt   System out println  boring          case  Thursday  - gt  System out println  getting better          case  Friday    Saturday    Sunday  - gt  System out println  much better

User · Answer

If you have a place in your code where you can switch on a String  then it may be better to refactor the String to be an enumeration of the possible values  which you can switch on  Of course  you limit the potential values of Strings you can have to those in the enumeration  which may or may not be desired   Of course your enumeration could have an entry for  other   and a fromString String  method  then you could have  ValueEnum enumval   ValueEnum fromString myString   switch  enumval       case MILK  lap    break     case WATER  sip    break     case BEER  quaff    break     case OTHER      default  dance    break

[java] Why can't I use switch statement on a String?

Examples related to java

Examples related to string

Examples related to switch-statement