What is the purpose of `boolean` type in JVM?

Question

As it said in JVMS8:

Although the Java Virtual Machine defines a boolean type, it only provides very limited support for it. There are no Java Virtual Machine instructions solely dedicated to operations on boolean values. Instead, expressions in the Java programming language that operate on boolean values are compiled to use values of the Java Virtual Machine int data type.

Indeed, these two methods:

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

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

will produce the same byte code (except the method signatures)

  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       

So, I do not understand why JVM needs boolean type. Is it just for the runtime check of method signatures?

Answer 1

As minimum it is needed to support methods overloading. Say, we have two methods in the same class

boolean a(boolean x) {...}

and

boolean a(int x) {...}

They can have different internal logic, so in the byte code they should be distinguished by their signatures.