java 如何检查字符串是否为空？
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How to check if String is empty?
提问by Subhrajyoti Majumder
I am using following code to check if the String is empty
我正在使用以下代码检查字符串是否为空
if( !Index2.toString().isEmpty()){
....
}
But I run into following error
但我遇到了以下错误
java.lang.NullPointerException
回答by Luiggi Mendoza
Your Index2variable has nullvalue. That's why you get the error. Specifically, the error is here:
你的Index2变量null有价值。这就是你得到错误的原因。具体来说，错误在这里：
Index2.toString()
Assuming your Index2variable is different from null, your code will work. In order to make your code to work, you can validate that your Index2is different from nullor add a try/catchblock that handles NullPointerException.
假设您的Index2变量不同于null，您的代码将起作用。为了使你的代码的工作，你可以验证你Index2是从不同null或添加try/catch块来处理NullPointerException。
First way:
第一种方式：
if( Index2 != null && !Index2.toString().isEmpty()){
//...
}
Second way:
第二种方式：
try {
if( !Index2.toString().isEmpty()){
//...
}
} catch (NullPointerException npe) {
//handle the Exception...
}
IMHO I would use the first way.
恕我直言，我会使用第一种方式。
回答by csk
Check for String not to be null as well check for the empty space in a String because even if we have a space in a String as myString=" "; myString.isEmpty() will return false . so please considering the case above i will suggest as :
检查 String 是否为 null 以及检查 String 中的空白空间，因为即使我们在 String 中有一个空格 myString=" "; myString.isEmpty() 将返回 false 。所以请考虑上面的情况，我会建议：
if (myString != null && myString.trim().length() != 0 )
return true;
回答by Pete
There's a StringUtils class in the apache.commons package that has lots of useful methods, like
apache.commons 包中有一个 StringUtils 类，它有很多有用的方法，比如
StringUtils.isEmpty(theString)
Which will do both comparisons, != null and isEmpty and looks better.
这将进行两种比较， != null 和 isEmpty 并且看起来更好。
回答by Subhrajyoti Majumder
Check Null also.
也检查 Null。
if( Index2!=null && !Index2.toString().isEmpty()){
....
}
回答by Ravi A
isEmpty()and nullhas nothing to do with each other. First checks the value of String if its equal to ""- OR you can say it will return true if its length is only and only 0. And second is checking for its initialization.
isEmpty()和null彼此无关。首先检查 String 的值是否等于""- 或者你可以说如果它的长度只有并且只有 0，它将返回 true。第二个是检查它的初始化。
You should check for both of these condition if needed, like this,
如果需要，您应该检查这两种情况，如下所示，
if( str != null && !str.isEmpty() ) { ... }
if( str != null && !str.isEmpty() ) { ... }
OR
或者
if( str != null && !str.equals("") ) { ... }
if( str != null && !str.equals("") ) { ... }
OR use this in your case,
或者在你的情况下使用这个，
if(index2 != null) { if( index2.toString() != null && !index2.toString().isEmpty() ) { ... } }
if(index2 != null) { if( index2.toString() != null && !index2.toString().isEmpty() ) { ... } }
回答by anubhava
This is how you should check empty for your case:
这是您应该如何为您的案例检查空：
if( Index2 == null || Index2.toString() == null ||
Index2.toString().length() == 0)
// it is empty
回答by Sumit Singh
Use The following code:
使用以下代码：
if(Index2!=null){
if( !Index2.toString().isEmpty()){
....
}
}
