Question

我遇到了这一行的问题（下面评论）：

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

输出false。

但是，System.out.println(s3==s4)输出true。

现在，我无法理解为什么会得到这个结果：

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));

在您的版本中，"Using == ::" + s3正在通过==与s4进行比较，这不是您想要的。

一般来说，+的{{3}}高于==，这就是"Using == ::" + s3==s4被评估为("Using == ::" + s3) == s4的原因。

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，您将 false 作为输出。

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

正如其他答案所说，你需要使用括号括起你的布尔表达式：

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)

修改给定代码的输出是：

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

打印字符串比较结果时得到奇怪的输出

3 个答案: