有人知道一个字符串
www+=空值的null后 为什么就表成wwwnull了
String s="www";
s+=null;
S最后的值是wwwnull
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因为这里把null当成字符串编译了吧
------解决方案--------------------
null是所有类的未实例化的一个对象，所以他可以转型成由低向上的转型。
如果转型的几个类是有上而下继承下来，null转成最低层的那个类。
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String Initializes
- Java code
public String() { this.offset = 0; this.count = 0; this.value = new char[0]; } public String(String original) { int size = original.count; char[] originalValue = original.value; char[] v; if (originalValue.length > size) { // The array representing the String is bigger than the new // String itself. Perhaps this constructor is being called // in order to trim the baggage, so make a copy of the array. int off = original.offset; v = Arrays.copyOfRange(originalValue, off, off+size); } else { // The array representing the String is the same // size as the String, so no point in making a copy. v = originalValue; } this.offset = 0; this.count = size; this.value = v; }