java - JVM 中 `boolean` 类型的用途是什么？

Question

因为它said在 JVMS8 中:

Although the Java Virtual Machine defines a boolean type, it only providesvery limited support for it. There are no Java Virtual Machine instructions solelydedicated to operations on boolean values. Instead, expressions in the Javaprogramming language that operate on boolean values are compiled to use valuesof the Java Virtual Machine int data type.

的确，这两个方法:

boolean expr1(boolean a, boolean b) {
    return a || b;
}

int expr2(int a, int b) {
    return ((a != 0) || (b != 0)) ? 1 : 0;
}

将产生相同的字节码(方法签名除外)

  boolean expr1(boolean, boolean);
    Signature: (ZZ)Z
    Code:
       0: iload_1       
       1: ifne          8
       4: iload_2       
       5: ifeq          12
       8: iconst_1      
       9: goto          13
      12: iconst_0      
      13: ireturn       

  int expr2(int, int);
    Signature: (II)I
    Code:
       0: iload_1       
       1: ifne          8
       4: iload_2       
       5: ifeq          12
       8: iconst_1      
       9: goto          13
      12: iconst_0      
      13: ireturn       

所以，我不明白为什么JVM 需要boolean 类型。是否仅用于方法签名的运行时检查？

Answer 1

至少需要支持方法重载。比如说，我们在同一个类中有两个方法

boolean a(boolean x) {...}

和

boolean a(int x) {...}

它们可以有不同的内部逻辑，所以在字节码中应该通过它们的签名来区分它们。