null被挟制转化为字符_J2SE

null被强制转化为字符？
String str=null;
System.out.println((str+="chen"));
输出结果为 nullchen
为什么呢？

------解决方案--------------------

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String str=null;
System.out.println((str+="chen"));
输出结果为 nullchen
为什么呢？

------解决方案--------------------
不好意思，这个解释文不对题，没仔细看LZ问题

String str=null;
System.out.println((str+="chen"));

等价于
String str=null;
System.out.println(new StringBuilder().append(str).append("chen").toString);

我们要看的是append方法的源码

Java code

public AbstractStringBuilder append(String str) {    if (str == null) str = "null";        int len = str.length();    if (len == 0) return this;    int newCount = count + len;    if (newCount > value.length)        expandCapacity(newCount);    str.getChars(0, len, value, count);    count = newCount;    return this;    }
------解决方案--------------------
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Prints a string. If the argument is null then the string "null" is printed. Otherwise, the string's characters are converted into bytes according to the platform's default character encoding, and the……