Java字符串问题

Question

我运行了以下程序，

    String firstString = "String";
    String secondString = "String";
    String thirdString = new String("String");
    System.out.println(firstString == secondString);
    System.out.println(firstString == thirdString);
    System.out.println(firstString.intern() == thirdString);
    System.out.println(firstString.intern() == thirdString.intern());
    System.out.println(firstString.intern().equals(thirdString.intern()));
    System.out.println(firstString == thirdString);

我的输出是

true
false
false
true
true
false

我了解到 jvm 将具有相同内容的字符串合并为相同的字符串。那正确吗？如果那是真的那么为什么 firstString == thirdString 不返回 false？ jvm 是否仅汇集仅使用 :""而不是使用 new 运算符初始化的字符串？

Answer 1

池仅与字符串文字相关 - 所以 firstString 和 secondString 实际上是同一个对象 - 而在 thirdString 中你明确要求要在堆上创建的新对象。

我建议阅读有关 string literals in the spec 的部分.

它提供了有关如何以及何时合并字符串的更多信息。

另外，请注意本节末尾的这些项目符号:

• Literal strings within the same class (§8) in the same package (§7) represent references to the same String object (§4.3.1).
• Literal strings within different classes in the same package represent references to the same String object.
• Literal strings within different classes in different packages likewise represent references to the same String object.
• Strings computed by constant expressions (§15.28) are computed at compile time and then treated as if they were literals.
• Strings computed by concatenation at run time are newly created and therefore distinct.