最近在使用java String中的方法substring(index)时发现传入一个参数index时,当index = str.length()并不报错,且返回一个空字符串。于是查阅了一下java的源代码,才发现原来如此:
substing()源码:
public String substring(int beginIndex) { if (beginIndex < 0) { throw new StringIndexOutOfBoundsException(beginIndex); } int subLen = value.length - beginIndex; if (subLen < 0) { throw new StringIndexOutOfBoundsException(subLen); } return (beginIndex == 0) ? this : new String(value, beginIndex, subLen); }可知只要 sublen可以为零,而new String()又是怎么工作的呢?
看以下的代码:
public String(char value[], int offset, int count) { if (offset < 0) { throw new StringIndexOutOfBoundsException(offset); } if (count <= 0) { if (count < 0) { throw new StringIndexOutOfBoundsException(count); } if (offset <= value.length) { this.value = "".value; return; } } // Note: offset or count might be near -1>>>1. if (offset > value.length - count) { throw new StringIndexOutOfBoundsException(offset + count); } this.value = Arrays.copyOfRange(value, offset, offset+count);
当count等于0的时候如果offset <= value.length 则生成一个空串;