java String的注意事项

1. +运算的区别

  public void test02(){
        String x = "abc";
        String y = "ab" + "c";
        System.out.println(x == y);

        String c = "ab";
        String d = "abc";
        // 相当于   String f = new StringBuilder(c).append("c").toString();
        String e = c + "c";

        System.out.println(c == e);
    }

编译后是：

 public void test02() {
        String x = "abc";
        String y = "abc";
        System.out.println(x == y);
        String c = "ab";
        String d = "abc";
        String e = c + "c";
        System.out.println(c == e);
    }

通过以上能够看出： String y = “ab” + “c”; 编译后变成了 String y = “abc”;而这个 String e = c + “c”; 相当于
String f = new StringBuilder©.append(“c”).toString(); 因此，打印返回 false