打印字符串比较结果时得到奇怪的输出

Question

我正面临着这条线的问题(下面评论):

System.out.println("Using == ::"+s3==s4)

哪个输出false.

但是,System.out.println(s3==s4)产出true.

现在,我无法理解为什么我得到这个结果:

public class string {
    public static void main(String[] args){
        String s3="Shantanu";
        String s4=s3;
        String s1=new String("java");
        String s2=new String("javaDeveloper");

        System.out.println("Using Equals Method::"+s1.equals(s2));
        System.out.println("Using Equals Method::"+s3.equals(s4));
        System.out.println("Using == ::"+s3==s4);//Problem is here in this line
        System.out.println(s1+"Directly printing the s2 value which is autocasted from superclass to string subclass ");
        System.out.println("Directly printing the s1 value which is autocasted from superclass to string subclass "+s2);
        System.out.println(s3);
    }
}

Output-Using Equals Method::false
Using Equals Method::true
Using == ::false
java Directly printing the s2 value which is autocasted from superclass to string subclass
Directly printing the s1 value which is autocasted from superclass to string subclass javaDeveloper

Answer 1

你错过了一组括号:

System.out.println("Using == ::" + (s3==s4));

在你的版本,"Using == ::" + s3正在通过比==对s4,这是不是你想要的.

一般情况下,+具有更高的优先级比==,这就是为什么"Using == ::" + s3==s4被评价为("Using == ::" + s3) == s4.

Answer 2

您正在使用此代码:

System.out.println("Using == ::"+ s3==s4);

正在评估为:

System.out.println( ("Using == ::" + s3) == s4);

因此,你输出的结果是假的.

原因是运算符优先级+高于==此Operator Precedence表:http://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html

正如其他答案所说,您需要使用包含布尔表达式的括号:

System.out.println("Using == ::" + (s3==s4));

Answer 3

这条线是正确的:

"Using == ::"+s3 不等于 s4

您需要更改代码:

"Using == ::"+(s3==s4)

编辑: 给定代码的输出是:

Using Equals Method::false
Using Equals Method::true
false
javaDirectly printing the s2 value which is autocasted from superclass to string subclass 
Directly printing the s1 value which is autocasted from superclass to string subclass javaDeveloper
Shantanu