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Value-specific class bodies in an enum

/ Published in: Java
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In covering the more advanced features of enums, I can't leave out the ability to define value-specific class bodies. That sounds sort of fancy, but all it means is that each enumerated value within a type can define value-specific methods.

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  1. // These are the the opcodes that our stack machine can execute.
  2.  
  3.    abstract static enum Opcode {
  4.  
  5.      PUSH(1),
  6.  
  7.      ADD(0),
  8.  
  9.      BEZ(1); // Remember the required semicolon after last enum value
  10.  
  11.  
  12.  
  13.      int numOperands;
  14.  
  15.  
  16.  
  17.      Opcode(int numOperands) { this.numOperands = numOperands; }
  18.  
  19.  
  20.  
  21.      public void perform(StackMachine machine, int[] operands) {
  22.  
  23.        switch(this) {
  24.  
  25.          case PUSH: machine.push(operands[0]); break;
  26.  
  27.          case ADD: machine.push(machine.pop( ) + machine.pop( )); break;
  28.  
  29.          case BEZ: if (machine.pop( ) == 0) machine.setPC(operands[0]); break;
  30.  
  31.          default: throw new AssertionError( );
  32.  
  33.        }
  34.  
  35.      }
  36.  
  37.    }

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