java – 添加String Literals和String对象之间的区别

添加String Literal和String Object之间有什么区别？

例如

    String s1 ="hello";
    String s2 ="hello1";
    String s3 ="hello" + "hello1";
    String s4 ="hellohello1";
    String s5 = s1 + s2;

    System.out.println(s3 == s4); // returns true
    System.out.println(s3 == s5); // return false
    System.out.println(s4 == s5); // return false

为什么s3 / s4没有指向与s5相同的位置？

解决方法:

因为s1 s2不是常量表达式,因为s1和s2不是final,因此它的结果不是interned,即创建另一个对象来表示它,因此引用比较产生false.

JLS 3.10.5 String Literals：

String literals-or, more generally, strings that are the values of constant expressions (§15.28)-are “interned” so as to share unique instances, using the method String.intern.

JLS 15.28 Constant Expression：

A compile-time constant expression is an expression denoting a value of primitive type or a String that does not complete abruptly and is composed using only the following:

• …
• Simple names that refer to constant variables (§4.12.4).

JLS 4.12.4定义了最终变量.

如果将s1和s2声明为final,则s3 == s5将为true.

标签：java,string,literals
来源： https://codeday.me/bug/20190730/1578910.html