Accessing constructor of an anonymous class

Question

Lets say I have a concrete class Class1 and I am creating an anonymous class out of it   Object a   new Class1            void someNewMethod                         Now is there any way I could overload the constructor of this anonymous class  Like shown below  Object a   new Class1            void someNewMethod                      public XXXXXXXX int a             super              System out println a                        With something at xxxxxxxx to name the constructor

User · Answer

That is not possible  but you can add an anonymous initializer like this   final int anInt        Object a   new Class1             System out println anInt          void someNewMethod              Don t forget final on declarations of local variables or parameters used by the anonymous class  as i did it for anInt

User · Answer

Peter Norvig s The Java IAQ  Infrequently Answered Questions  http   norvig com java-iaq html constructors - Anonymous class contructors  http   norvig com java-iaq html init - Construtors and initialization  Summing  you can construct something like this    public class ResultsBuilder       Set lt Result gt  errors      Set lt Result gt  warnings            public Results lt E gt  build             return new Results lt E gt                  private Result   errorsView              private Result   warningsView                                errorsView   ResultsBuilder this getErrors                    warningsView   ResultsBuilder this getWarnings                               public Result   getErrors                     return errorsView                             public Result   getWarnings                     return warningsView                                      public Result   getErrors             return  isEmpty this errors    errors toArray new Result 0     null             public Result   getWarnings             return  isEmpty this warnings    warnings toArray new Result 0     null

User · Answer

It doesn t make any sense to have a named overloaded constructor in an anonymous class  as there would be no way to call it  anyway   Depending on what you are actually trying to do  just accessing a final local variable declared outside the class  or using an instance initializer as shown by Arne  might be the best solution

User · Answer

In my case  a local class  with custom constructor  worked as an anonymous class   Object a   getClass1 x    public Class1 getClass1 int x      class Class2 implements Class1       void someNewMethod              public Class2 int a         super          System out println a               Class1 c   new Class2 x     return c

User · Answer

If you dont need to pass arguments  then initializer code is enough  but if you need to pass arguments from a contrcutor there is a way to solve most of the cases   Boolean var  new anonymousClass        private String myVar    String for example       Overriden public Boolean method int i               use myVar and i           public String setVar String var  myVar var  return this     Returns self instane   setVar  Hello   method 3

User · Answer

Peter Norvig s The Java IAQ  Infrequently Answered Questions  http   norvig com java-iaq html constructors - Anonymous class contructors  http   norvig com java-iaq html init - Construtors and initialization  Summing  you can construct something like this    public class ResultsBuilder       Set lt Result gt  errors      Set lt Result gt  warnings            public Results lt E gt  build             return new Results lt E gt                  private Result   errorsView              private Result   warningsView                                errorsView   ResultsBuilder this getErrors                    warningsView   ResultsBuilder this getWarnings                               public Result   getErrors                     return errorsView                             public Result   getWarnings                     return warningsView                                      public Result   getErrors             return  isEmpty this errors    errors toArray new Result 0     null             public Result   getWarnings             return  isEmpty this warnings    warnings toArray new Result 0     null

User · Answer

You can have a constructor in the abstract class that accepts the init parameters  The Java spec only specifies that the anonymous class  which is the offspring of the  optionally  abstract class or implementation of an interface  can not have a constructor by her own right   The following is absolutely legal and possible   static abstract class Q      int z      Q int z   this z z       void h            Q me   new Q 1                         If you have the possibility to write the abstract class yourself  put such a constructor there and use fluent API where there is no better solution  You can this way override the constructor of your original class creating an named sibling class with a constructor with parameters and use that to instantiate your anonymous class

User · Answer

In my case  a local class  with custom constructor  worked as an anonymous class   Object a   getClass1 x    public Class1 getClass1 int x      class Class2 implements Class1       void someNewMethod              public Class2 int a         super          System out println a               Class1 c   new Class2 x     return c

User · Answer

From the Java Language Specification  section 15 9 5 1      An anonymous class cannot have an   explicitly declared constructor    Sorry     EDIT  As an alternative  you can create some final local variables  and or include an instance initializer in the anonymous class  For example   public class Test       public static void main String   args  throws Exception           final int fakeConstructorArg   10           Object a   new Object                                   System out println  arg       fakeConstructorArg                                      It s grotty  but it might just help you  Alternatively  use a proper nested class

User · Answer

Here s another way around the problem   public class Test       public static final void main String   args            new Thread                 private String message   null               Thread initialise String message                    this message   message                  return this                             public void run                    System out println message                           initialise args 0   start

User · Answer

It doesn t make any sense to have a named overloaded constructor in an anonymous class  as there would be no way to call it  anyway   Depending on what you are actually trying to do  just accessing a final local variable declared outside the class  or using an instance initializer as shown by Arne  might be the best solution

User · Answer

I know the thread is too old to post an answer  But still i think it is worth it   Though you can t have an explicit constructor  if your intention is to call the constructor of the super class  then the following is all you have to do   StoredProcedure sp   new StoredProcedure datasource  spName            init code if there are any       This is an example of creating a StoredProcedure object in Spring by passing a DataSource and a String object   So the Bottom line is  if you want to create an anonymous class and want to call the super class constructor then create the anonymous class with a signature matching the super class constructor

User · Answer

From the Java Language Specification  section 15 9 5 1      An anonymous class cannot have an   explicitly declared constructor    Sorry     EDIT  As an alternative  you can create some final local variables  and or include an instance initializer in the anonymous class  For example   public class Test       public static void main String   args  throws Exception           final int fakeConstructorArg   10           Object a   new Object                                   System out println  arg       fakeConstructorArg                                      It s grotty  but it might just help you  Alternatively  use a proper nested class

User · Answer

That is not possible  but you can add an anonymous initializer like this   final int anInt        Object a   new Class1             System out println anInt          void someNewMethod              Don t forget final on declarations of local variables or parameters used by the anonymous class  as i did it for anInt

User · Answer

I know the thread is too old to post an answer  But still i think it is worth it   Though you can t have an explicit constructor  if your intention is to call the constructor of the super class  then the following is all you have to do   StoredProcedure sp   new StoredProcedure datasource  spName            init code if there are any       This is an example of creating a StoredProcedure object in Spring by passing a DataSource and a String object   So the Bottom line is  if you want to create an anonymous class and want to call the super class constructor then create the anonymous class with a signature matching the super class constructor

User · Answer

It doesn t make any sense to have a named overloaded constructor in an anonymous class  as there would be no way to call it  anyway   Depending on what you are actually trying to do  just accessing a final local variable declared outside the class  or using an instance initializer as shown by Arne  might be the best solution

User · Answer

If you dont need to pass arguments  then initializer code is enough  but if you need to pass arguments from a contrcutor there is a way to solve most of the cases   Boolean var  new anonymousClass        private String myVar    String for example       Overriden public Boolean method int i               use myVar and i           public String setVar String var  myVar var  return this     Returns self instane   setVar  Hello   method 3

User · Answer

From the Java Language Specification  section 15 9 5 1      An anonymous class cannot have an   explicitly declared constructor    Sorry     EDIT  As an alternative  you can create some final local variables  and or include an instance initializer in the anonymous class  For example   public class Test       public static void main String   args  throws Exception           final int fakeConstructorArg   10           Object a   new Object                                   System out println  arg       fakeConstructorArg                                      It s grotty  but it might just help you  Alternatively  use a proper nested class

User · Answer

From the Java Language Specification  section 15 9 5 1      An anonymous class cannot have an   explicitly declared constructor    Sorry     EDIT  As an alternative  you can create some final local variables  and or include an instance initializer in the anonymous class  For example   public class Test       public static void main String   args  throws Exception           final int fakeConstructorArg   10           Object a   new Object                                   System out println  arg       fakeConstructorArg                                      It s grotty  but it might just help you  Alternatively  use a proper nested class

User · Answer

Here s another way around the problem   public class Test       public static final void main String   args            new Thread                 private String message   null               Thread initialise String message                    this message   message                  return this                             public void run                    System out println message                           initialise args 0   start

User · Answer

You can have a constructor in the abstract class that accepts the init parameters  The Java spec only specifies that the anonymous class  which is the offspring of the  optionally  abstract class or implementation of an interface  can not have a constructor by her own right   The following is absolutely legal and possible   static abstract class Q      int z      Q int z   this z z       void h            Q me   new Q 1                         If you have the possibility to write the abstract class yourself  put such a constructor there and use fluent API where there is no better solution  You can this way override the constructor of your original class creating an named sibling class with a constructor with parameters and use that to instantiate your anonymous class

User · Answer

It doesn t make any sense to have a named overloaded constructor in an anonymous class  as there would be no way to call it  anyway   Depending on what you are actually trying to do  just accessing a final local variable declared outside the class  or using an instance initializer as shown by Arne  might be the best solution

User · Answer

Yes   It is right that you can not define construct in an Anonymous class but it doesn t mean that anonymous class don t have constructor  Confuse     Actually you can not define construct in an Anonymous class but compiler generates an constructor for it with the same signature as its parent constructor called  If the parent has more than one constructor  the anonymous will have one and only one constructor

User · Answer

Yes   It is right that you can not define construct in an Anonymous class but it doesn t mean that anonymous class don t have constructor  Confuse     Actually you can not define construct in an Anonymous class but compiler generates an constructor for it with the same signature as its parent constructor called  If the parent has more than one constructor  the anonymous will have one and only one constructor

User · Answer

That is not possible  but you can add an anonymous initializer like this   final int anInt        Object a   new Class1             System out println anInt          void someNewMethod              Don t forget final on declarations of local variables or parameters used by the anonymous class  as i did it for anInt

User · Answer

That is not possible  but you can add an anonymous initializer like this   final int anInt        Object a   new Class1             System out println anInt          void someNewMethod              Don t forget final on declarations of local variables or parameters used by the anonymous class  as i did it for anInt

[java] Accessing constructor of an anonymous class

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