Java字符串池对象创建

Question

我怀疑我的概念在字符串池中是否清晰.请研究以下一组代码,并检查我的答案在以下一组陈述后创建的对象数量是否正确: -

1)

String s1 = "abc";
String s2 = "def";
s2 + "xyz";

2)

 String s1 = "abc";
 String s2 = "def";
 s2 = s2 + "xyz";

3)

String s1 = "abc";
String s2 = "def";
String s3 = s2 + "xyz";

4)

String s1 = "abc";
String s2 = "def";
s2 + "xyz";
String s3 = "defxyz";

根据我所知的概念,在上面的4个案例中,在执行每组行之后将创建4个对象.

Answer 1

你不能拥有s2 + "xyz"自己的表达方式.编译器仅评估常量,并且只有字符串常量会自动添加到字符串文字池中.

例如

final String s1 = "abc"; // string literal
String s2 = "abc"; // same string literal

String s3 = s1 + "xyz"; // constants evaluated by the compiler 
                        // and turned into "abcxyz"

String s4 = s2 + "xyz"; // s2 is not a constant and this will
                        // be evaluated at runtime. not in the literal pool.
assert s1 == s2;
assert s3 != s4; // different strings.