是否使用+串联创建的字符串存储在字符串池中？ [英] Are strings created with + concatenation stored in the string pool?

问题描述

例如

 String s = "Hello" + " World";

我知道池中有两个字符串Hello和World但是，确实： Hello World进入字符串池？

I know there are two strings in the pool "Hello" and "World" but, does: "Hello World" go into the string pool?

如果是这样，那该怎么办？

If so, what about?

String s2 = new String("Hola") + new String(" Mundo");

每种情况下池中有多少个字符串？

How many strings are there in the pool in each case?

推荐答案

是的，如果通过连接两个 String String $ c> 文字它也将被实习。

Yes, if a String is formed by concatenating two String literals it will also be interned.

来自JLS：

因此，测试程序包含
编译单元（§7.3）：

Thus, the test program consisting of the compilation unit (§7.3):

package testPackage;
class Test {
    public static void main(String[] args) {
        String hello = "Hello", lo = "lo"; 
        System.out.print((hello == "Hello") + " "); // 1
        System.out.print((Other.hello == hello) + " "); // 2
        System.out.print((other.Other.hello == hello) + " "); // 3
        System.out.print((hello == ("Hel"+"lo")) + " "); // 4
        System.out.print((hello == ("Hel"+lo)) + " "); // 5
        System.out.println(hello == ("Hel"+lo).intern()); // 6
    }
}
class Other { static String hello = "Hello"; }
and the compilation unit:
package other;
public class Other { static String hello = "Hello"; }

产生输出：

true  //-> 1
true  //-> 2
true  //-> 3
true  //-> 4
false //-> 5
true  //-> 6

重要的行是4和5. 4代表你在第一种情况下的要求;图5显示了如果一个不是文字（或更一般地，编译时常量）会发生什么。

The important lines are 4 and 5. 4 represents what you are asking in the first case; 5 shows you what happens if one is not a literal (or more generally, a compile-time constant).

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