字符串JAVA内存问题疑惑

Question

对内存不是特别了解，一直有个疑惑，String a ="a ";String b="b";String c="ab";那么String c ==a+"b";为false，字符串常量池中有个a了，为什么这里的a地址变了？有哪位详解一下！

Answer 1

String a ="a";String b="b";String c="ab".intern(); String d=(a+"b").intern(); System.out.println(c==d); 结果 true
必须调用intern() 方法才能把字符串放到常量池里。
这是官方文档对intern() 的描述
Returns a canonical representation for the string object.

A pool of strings, initially empty, is maintained privately by the class String.

When the intern method is invoked, if the pool already contains a string equal to this String object as determined by the equals(Object) method, then the string from the pool is returned. Otherwise, this String object is added to the pool and a reference to this String object is returned.

It follows that for any two strings s and t, s.intern() == t.intern() is true if and only if s.equals(t) is true.

All literal strings and string-valued constant expressions are interned. String literals are defined in section 3.10.5 of the The Java™ Language Specification.

Returns:
a string that has the same contents as this string, but is guaranteed to be from a pool of unique strings.