java中String字符串==的疑问？

Question

java中String字符串==的疑问？谁能帮忙解释和理解一下！顺便说一下底层的原理和运行规则？
直接po代码和截图

public class TestString {

    /** 
    * 测试String
    */
    public static void main(String[] args) {
        String a = "hello2";
        final String b = getStr2();
        String c = b + 2;
        String d = "hello2";
        String e = new String("hello2");
        String f = new String("hello2");
        String h = "hello";
        String j = h + 2;
        StringBuffer sb = new StringBuffer("hello2");
        StringBuilder sb2 = new StringBuilder("hello2");
        String k = getStr2();
        String m = k + 2;
        System.out.println("c结果" + (a == c));
        System.out.println("d结果" + (a == d));
        System.out.println("e结果" + (a == e));
        System.out.println("f结果" + (a == f));
        System.out.println("f.toString()结果" + (a == f.toString()));
        System.out.println("j结果" + (a == j));
        System.out.println("sb.toString()结果" + (a == sb.toString()));
        System.out.println("sb2.toString()结果" + (a == sb2.toString()));
        System.out.println("m结果" + (a == m));
    }

    public static String getStr() {
        String text = "hello";
        return text;
    }

    public static String getStr2() {
        return "hello";
    }

}

Answer 1

String是引用类型，可以理解为c语言的指针，即其是指向某个地址的值，d结果为true是因为原来池里面已经有了估a和d指向的是同一个地址的值，如果是判断值是否相等可以用equals