老师您好，为什么这类System.out.println("a等于b：" + (a == b));打印出来的结果会是布尔值呢，在哪里写着boolean了呢

public class HelloWorld{

    public static void main(String[] args) {

int a=16;

double b=9.5;

String str1="hello";

String str2="imooc";

System.out.println("a等于b：" + (a ==  b));

System.out.println("a大于b：" + (a >  b));

System.out.println("a小于等于b：" + (a  <= b));

System.out.println("str1等于str2：" + (str1 ==  str2));

}

}