空字符串和空字符串的区别 [英] Difference between null and empty string

问题描述

空字符串 (String s = null) 和空字符串 (String s = "") 有什么区别?

What is the difference between a null string (String s = null) and an empty string (String s = "")?

这就是我所拥有的:

String s1 = ""; //print statement does not print any thing for s1 but s1.length()=0
String s2 = null;//print statement prints "null" for s2  but s2.length() gives exception

什么意思?

推荐答案

String s1 = ""; 表示将空的 String 分配给 s1.在这种情况下，s1.length() 与 "".length() 相同，它将按预期产生 0.

String s1 = ""; means that the empty String is assigned to s1. In this case, s1.length() is the same as "".length(), which will yield 0 as expected.

String s2 = null; 表示将 (null) 或根本没有值"分配给 s2.所以这个，s2.length() 与 null.length() 相同，这将产生 NullPointerException 因为你不能在 Java 中调用 null 变量(指针，排序)的方法.

String s2 = null; means that (null) or "no value at all" is assigned to s2. So this one, s2.length() is the same as null.length(), which will yield a NullPointerException as you can't call methods on null variables (pointers, sort of) in Java.

还有一点，声明

String s1;

其实效果一样:

String s1 = null;

然而

String s1 = "";

正如所说，是另一回事.

Is, as said, a different thing.

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