JVM 中 String 对象的分配

如下的输出值都是什么

  static void t1() {
    String str2 = new String("str01");
    str2.intern();
    String str1 = "str01";
    System.out.println(str2==str1);
  }

  static void t2() {
    String str2 = new String("str01");
    String str3 = str2.intern();
    String str1 = "str01";
    System.out.println(str2==str1);
    System.out.println(str3==str1);
  }

  static void t4() {
    String str2 = new String("str") + new String("01");
    String str1 = "str01";
    String str3 = str2.intern();
    System.out.println(str2==str1);
    System.out.println(str3==str1);
  }

  static void t3() {
    String str2 = new String("str")+new String("01");
//    String str3 = str2.intern();
    str2.intern();
    String str1 = "str01";
    System.out.println(str2==str1);
//    System.out.println(str3==str1);
  }

  static void t5() {
    String s1 = "Programming";
    String s3 = "Program";
    String s4 = "ming";
    String s6 = s3 + s4;
    System.out.println(s1 == s6);
  }

  static void t6() {
    String s1 = "Programming";
    final String s3 = "Program";
    final String s4 = "ming";
    String s6 = s3 + s4;
    System.out.println(s1 == s6);
  }

    String s1 = "Programming";
    String s3 = "Program";
    String s4 = "ming";
    String s6 = s3 + s4;
    System.out.println(s1 == s6);

通过 javap -c 进行反编译发现底层通过调用 StringBuilder.append 进行拼接后调用 toString 方法，所以 s6 对象是在生成在【堆】中，所以返回 false

  static void t6() {
    String s1 = "Programming";
    final String s3 = "Program";
    final String s4 = "ming";
    String s6 = s3 + s4;
    System.out.println(s1 == s6);
  }

通过 javap -c 进行反编译发现底层通过将变量 s3,s4 替换成了对应字符串，所以 s6 对象也是在常量池中