Java SE7新特性之二进制字面量

 Java SE 7中, 整数类型(byte, short, int以及long) 也可以使用二进制数系来表示。要指定一个二进制字面量，可以给二进制数字添加前缀 0b 或者 0B。下面的示例展示了一些二进制字面量：

     // 一个8位的'byte'值:
     byte aByte = (byte)0b00100001;

     // 一个16位的'short'值:
     short aShort = (short)0b1010000101000101;

     // 几个32位的'int'值:
     int anInt1 = 0b10100001010001011010000101000101;
     int anInt2 = 0b101;
     int anInt3 = 0B101; // B可以是大写或者小写.

     // 一个64位的'long'值.注意"L"后缀:
     long aLong = 0b1010000101000101101000010100010110100001010001011010000101000101L;

         相比于十六进制或者八进制，二进制字面量可以使数据之间的关系更加清晰。比如, 下面数组中的每个后续数字是按位旋转的：

     public static final int[] phases = {
       0b00110001,
       0b01100010,
       0b11000100,
       0b10001001,
       0b00010011,
       0b00100110,
       0b01001100,
       0b10011000
     }

         十六进制中, 数字之间的关系并不清晰:

     public static final int[] phases = {
       0x31, 0x62, 0xC4, 0x89, 0x13, 0x26, 0x4C, 0x98
     }

         可以在代码中使用二进制字面量常量来验证一个规范文档, 比如一个针对假设的8位微处理器的模拟器:

     public State decodeInstruction(int instruction, State state) {
       if ((instruction & 0b11100000) == 0b00000000) {
          final int register = instruction & 0b00001111;
          switch (instruction & 0b11110000) {
            case 0b00000000: return state.nop();
            case 0b00010000: return state.copyAccumTo(register);
            case 0b00100000: return state.addToAccum(register);
            case 0b00110000: return state.subFromAccum(register);
            case 0b01000000: return state.multiplyAccumBy(register);
            case 0b01010000: return state.divideAccumBy(register);
            case 0b01100000: return state.setAccumFrom(register);
            case 0b01110000: return state.returnFromCall();
            default: throw new IllegalArgumentException();
          }
       } else {
          final int address = instruction & 0b00011111;
          switch (instruction & 0b11100000) {
            case 0b00100000: return state.jumpTo(address);
            case 0b01000000: return state.jumpIfAccumZeroTo(address);
            case 0b01000000: return state.jumpIfAccumNonzeroTo(address);
            case 0b01100000: return state.setAccumFromMemory(address);
            case 0b10100000: return state.writeAccumToMemory(address);
            case 0b11000000: return state.callTo(address);
            default: throw new IllegalArgumentException();
          }
       }
     }

         可以使用二进制字面量增强位图的可读性:

     public static final short[] HAPPY_FACE = {
       (short)0b0000011111100000,
       (short)0b0000100000010000,
       (short)0b0001000000001000,
       (short)0b0010000000000100,
       (short)0b0100000000000010,
       (short)0b1000011001100001,
       (short)0b1000011001100001,
       (short)0b1000000000000001,
       (short)0b1000000000000001,
       (short)0b1001000000001001,
       (short)0b1000100000010001,
       (short)0b0100011111100010,
       (short)0b0010000000000100,
       (short)0b0001000000001000,
       (short)0b0000100000010000,
       (short)0b0000011111100000
     }

     本文翻译自Oracle官方文档http://docs.oracle.com/javase/7/docs/technotes/guides/language/binary-literals.html,如有不正确的地方，敬请指正，谢谢！

 

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