Java 空指针访问：该位置的变量只能为空
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Null pointer access: The variable can only be null at this location
提问by sky
for(int i=0;i<n;i++){
for(int j=0;j<26;j++){
if(str.charAt(i)== strChar.charAt(j) )
* strSet1.append(str.charAt(i));
}
* strSet2.append(str.charAt(i));
}
Exception:
例外：
Exception in thread "main" java.lang.NullPointerException
at AterSeries.main(AterSeries.java:33)
why this code gives null pointer exception
为什么这段代码给出了空指针异常
warning: Null pointer access: The variable strSet1 can only be null at this location Null pointer access: The variable strSet2 can only be null at this location
警告：空指针访问：变量 strSet1 在此位置只能为空 空指针访问：变量 strSet2 在此位置只能为空
采纳答案by t0mppa
Are strSet1and strSet2initialized before this? If they are null, you'd get a NullPointerException.
都strSet1和strSet2这之前初始化？如果它们为空，你会得到一个NullPointerException.
* EDIT *
* 编辑 *
You cannot call .append()(or any other method) on a variable that is null. Initialize them as:
你不能.append()在一个变量上调用（或任何其他方法）null。将它们初始化为：
StringBuffer strSet1 = new StringBuffer();
StringBuffer strSet2 = new StringBuffer();
