字符串等于和==，带有字符串串联

Question

我试图理解字符串比较与字符串比较的输出。需要明确的是，我拥有使用==和equals比较两个字符串的类。我试图将==和equals（）的输出合并为字符串。equals（）的输出会连续显示，但==的输出不会 连续显示。使用Java的装箱功能，将与字符串连接的布尔值联系起来。equals和==都返回布尔值。那么为什么会有这种差异呢？有人可以解释吗？

public class StringHandler {

    public void compareStrings() {
        String s1 = new String("jai");
        String s2 = "jai";
        String s3 = "jai";
        System.out.println("Object and literal compare by double equal to :: "
                + s1 == s2);
        System.out.println("Object and literal compare by equals :: "
                + s1.equals(s2));
        System.out
                .println("Literal comparing by double equal to :: " + s2 == s3);
        System.out.println("Literal comparing by equals :: " + s2.equals(s3));
    }

    public static void main(String[] args) {
        StringHandler sHandler = new StringHandler();
        sHandler.compareStrings();
    }
}

输出

false
Object and literal compare by equals :: true
false
Literal compareing by equals :: true

更新：答案

如果不使用s1 == s2的括号，则JVM将字符串比较为“对象和文字的文字乘以double等于:: jai” ==“ jai”，结果为 false
。因此，不会打印sysout中的实际内容。添加括号后，JVM会将字符串比较为“ jai” ==“ jai”，结果为

Object and literal compare by double equal to :: true

Answer 1

当你做

System.out.println("Object and literal compare by double equal to :: "
            + s1 == s2);

您首先将字符串"Object and literal compare by double equal to :: "与字符串连接s1，这将给

"Object and literal compare by double equal to :: jai"

然后，您要检查此字符串是否是与以下对象相同的对象（相同的引用）s2：

"Object and literal compare by double equal to :: jai" == "jai"

将会是false（输出将是false）。

换句话说，这是因为 运算符Priority 。一种“操纵”运算符优先级的方法是使用括号。括号内的运算将首先被解析：

System.out.println("Object and literal compare by double equal to :: " + (s1 == s2));