这样子是什么错误

编译的时候可以通过,可运行的时候出现如下这个画面
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Exception in thread"main"java.lang.NullPointerException
at Notepad2.initEventListener<Notepad2.java:199>
at Notepad2.<init><Notepad2.java:15>
at Notepad2.main<Notepad2.java:224>
Press any key to continue...
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空指针错误
Thrown when an application attempts to use null in a case where an object is required. These include:

Calling the instance method of a null object.
Accessing or modifying the field of a null object.
Taking the length of null as if it were an array.
Accessing or modifying the slots of null as if it were an array.
Throwing null as if it were a Throwable value.
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那要怎么避免或改呢?
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能用ＥＣＬＩＰ调试出最好，也可以检查一下哪里出错，是不是有的变量可能取ＮＵＬＬ值，后面引用又用到这个变量，而你没有处理

避免就是要细心喽，呵呵

愚见，见笑．
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