System.ArrayCopy , NullPointerException异常

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 byte[] partByte = null;if ((len =fileInputStream.read(buffer)) != -1) {System.arraycopy(buffer, 0 , partByte , 0, len);

报错，因为partByte是null，而后改成：

 byte[] partByte = null;int len;
// int count=0;try {if ((len =fileInputStream.read(buffer)) != -1) {if (len != 1024*1024) {byte[] bytes = new byte[len];System.arraycopy(buffer, 0 , bytes, 0, len);      partByte = bytes;

参考

String[] a = {"a","b","c","d","e"};
String[] b = null;
//System.arraycopy(a, 0, b, 0, 5); 　　　　//java.lang.NullPointerException
b = Arrays.copyOf(a, 5);     　　　　　　　//b={"a","b","c","d","e"}

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