OR operator in switch-case

Question

Let s take a simple switch-case that looks like    Override public void onClick View v        switch  v getId              case R id someValue           case R id someOtherValue                 do stuff             break            I wonder why it is not allowed to use the    operator  Like  switch  v getId          case R id someValue    R id someOtherValue             do stuff         break      The switch-case construct is pretty similar to an if-else statement  you can use the OR operator in an if however  What are the backgrounds for a switch-case to not accept this operator

User · Answer

Switch is not same as if-else-if    Switch is used when there is one expression that gets evaluated to a value and that value can be one of predefined set of values  If you need to perform multiple boolean   comparions operations run-time then if-else-if needs to be used

User · Answer

You cannot use    operators in between 2 case  But you can use multiple case values without using a break between them  The program will then jump to the respective case and then it will look for code to execute until it finds a  break   As a result these cases will share the same code   switch value          case 0       case 1              do stuff for if case 0    case 1          break          other cases      default           break

User · Answer

dude do like this       case R id someValue       case R id someOtherValue            do stuff   This is same as using OR operator between two values  Because of this case operator isn t there in switch case

User · Answer

What are the backgrounds for a switch-case to not accept this operator    Because case requires constant expression as its value  And since an    expression is not a compile time constant  it is not allowed   From JLS Section 14 11   Switch label should have following syntax      SwitchLabel        case ConstantExpression          case EnumConstantName          default       Under the hood   The reason behind allowing just constant expression with cases can be understood from the JVM Spec Section 3 10 - Compiling Switches      Compilation of switch statements uses the tableswitch and lookupswitch instructions  The tableswitch instruction is used when the cases of the switch can be efficiently represented as indices into a table of target offsets  The default target of the switch is used if the value of the expression of the switch falls outside the range of valid indices     So  for the cases label to be used by tableswitch as a index into the table of target offsets  the value of the case should be known at compile time  That is only possible if the case value is a constant expression  And    expression will be evaluated at runtime  and the value will only be available at that time   From the same JVM section  the following switch-case   switch  i        case 0   return  0      case 1   return  1      case 2   return  2      default  return -1      is compiled to   0   iload 1                Push local variable 1  argument i  1   tableswitch 0 to 2     Valid indices are 0 through 2   NOTICE This instruction         0  28                If i is 0  continue at 28       1  30                If i is 1  continue at 30       2  32                If i is 2  continue at 32       default 34           Otherwise  continue at 34 28  iconst 0               i was 0  push int constant 0    29  ireturn                   and return it 30  iconst 1               i was 1  push int constant 1    31  ireturn                   and return it 32  iconst 2               i was 2  push int constant 2    33  ireturn                   and return it 34  iconst m1              otherwise push int constant -1    35  ireturn                   and return it   So  if the case value is not a constant expressions  compiler won t be able to index it into the table of instruction pointers  using tableswitch instruction

User · Answer

foreach  array  one    two    three   as  v        switch   v            case  function   v                if   v     two   return  v              return  one               v               echo   v min  n               break              this works fine for languages supporting enclosures

[java] OR operator in switch-case?

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