null和空字符串之间的区别 [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 =）？

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

这是什么意思？

推荐答案

String s1 =; 表示空字符串已分配给 S1 。
在这种情况下， s1.length（）与。length（）相同，这将按预期产生 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（ null ）或没有任何价值被分配给 s2 。所以这个， s2.length（）与 null.length（）相同，这将产生一个 NullPointerException 因为你无法用Java调用 null 变量（指针，排序）上的方法。

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.

另外，一个点，声明

String s1;

实际上具有与以下相同的效果：

Actually has the same effect as:

String s1 = null;

然而

String s1 = "";

如上所述，是另一回事。

Is, as said, a different thing.

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