String x = "abcdef";
int begin=1;
int end=3;
x = x.substring(begin, end);
System.out.println(x);
bc
图1
private final char value[];
private final int offset;
private final int count;
// JDK6,包级私有构造,共享 value数组提升速度
String(int offset, int count, char value[]) {
this.value = value;
this.offset = offset;
this.count = count;
}
public String substring(int beginIndex, int endIndex) {
// ... 检查边界的代码
// 如果范围和自己一模一样,则返回自身,否则用value字符数组构造一个新的对象
return ((beginIndex == 0) && (endIndex == count)) ? this :
new String(offset + beginIndex, endIndex - beginIndex, value);
}
x = x.substring(begin, end) + "";
// JDK 7, 权限变为 public
public String(char value[], int offset, int count) {
// ... 检查边界..
// value 数组拷贝
this.value = Arrays.copyOfRange(value, offset, offset+count);
}
public String substring(int beginIndex, int endIndex) {
// ... 检查边界..
int subLen = endIndex - beginIndex;
// 如果和自身一样,那就返回自身,否则返回构造的新对象
return ((beginIndex == 0) && (endIndex == value.length)) ? this
: new String(value, beginIndex, subLen);
}
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