filtering JAVAC.STRINGSWITCH

This page discusses a not yet available feature!

Description

Starting from Java 7 possible to use String object in the expression of switch statement. In such case compiler generates additional switch that uses hashCode and additional conditions that use equals.

• https://stackoverflow.com/questions/25568639/why-switch-on-string-compiles-into-two-switches

Filtering

Source Example

switch (x) {
  case "AaAa":
    // case 1
    break;
  case "BBBB":
    // case 2
    break;
}

Bytecode Pattern

javac 1.8.0_121

 ...
 INVOKEVIRTUAL java/lang/String.hashCode ()I
 LOOKUPSWITCH
   2031744: L1
   default: L2
L1
 ALOAD 2
 LDC "BBBB"
 INVOKEVIRTUAL java/lang/String.equals (Ljava/lang/Object;)Z
 IFEQ L3
 ICONST_1
 ISTORE 3
 GOTO L2
L3
 ALOAD 2
 LDC "AaAa"
 INVOKEVIRTUAL java/lang/String.equals (Ljava/lang/Object;)Z
 IFEQ L2
 ICONST_0
 ISTORE 3
L2
 ILOAD 3
 LOOKUPSWITCH
   0: C1
   1: C2
   default: L4
C1:
 // case 1
 goto L4
C2:
 // case 2
L4
 ...

ecj 4.6.1

 INVOKEVIRTUAL java/lang/String.hashCode ()I
 LOOKUPSWITCH
   2031744: L1
   default: L2
L1:
 ALOAD 2
 LDC "AaAa"
 INVOKEVIRTUAL java/lang/String.equals (Ljava/lang/Object;)Z
 IFNE C1
 ALOAD 2
 LDC "BBBB"
 INVOKEVIRTUAL java/lang/String.equals (Ljava/lang/Object;)Z
 IFNE C2
 GOTO L2 
C1:
 // case 1
 GOTO L2
C2:
 // case 2
L2:
 ...