java - 需要有关此 Java 输出的帮助

Question

这个问题已经有答案了:

a confusion about java String literal pool and String's concatenation (4 个回答)

已关闭 8 年前。

这是一个非常简单的代码:

  public class Test2 {

public static void main(String[] args)  {
        String a = "hello2"; 
        final String b = "hello";
        String d = "hello";
        String c = b + 2; 
        String e = d + 2;
        System.out.println((a));
        System.out.println((c));
        System.out.println((e));
        System.out.println((a == c));
        System.out.println((a == e));

    }
}

输出是:

hello2
hello2
hello2
true
false

请告诉我为什么最后一个是“假”？谢谢

Answer 1

public static void main(String[] args)  {
        String a = "hello2"; 
        final String b = "hello"; // this will be a compile-time constant. `final String` makes a string compile-time-constant.
        String d = "hello";
        String c = b + 2; // The compiler will replace b+2 by "hello2"
        String e = d + 2; // d is not final. Hence value of b will be calculated at runtime.
        System.out.println((a));
        System.out.println((c));
        System.out.println((e));
        System.out.println((a == c));
        System.out.println((a == e));

    }