String 类定义：
public final class String
implements java.io.Serializable, Comparable<String>, CharSequence
/** 底层字符的存储*/
private final char value[];
/** 哈希码*/
private int hash; // Default to 0
private static final long serialVersionUID = -6849794470754667710L;
String类被声明为final的，意味着它不可以被继承。同时内部保持着了一个final 类型的char[]数组。
构造函数
public String(String original) {
this.value = original.value;
this.hash = original.hash;
}
public String(char value[]) {
this.value = Arrays.copyOf(value, value.length);
}
public String(char value[], int offset, int count) {
this.value = Arrays.copyOfRange(value, offset, offset+count);
}
其他方法
public int length() {
return value.length;
}
public boolean isEmpty() {
return value.length == 0;
}
public char charAt(int index) {
if ((index < 0) || (index >= value.length)) {
throw new StringIndexOutOfBoundsException(index);
}
return value[index];
}
public String substring(int beginIndex, int endIndex) {
int subLen = endIndex - beginIndex;
if (subLen < 0) {
throw new StringIndexOutOfBoundsException(subLen);
}
return ((beginIndex == 0) && (endIndex == value.length)) ? this
: new String(value, beginIndex, subLen);
}
// 复制区间:从offset到offset+count处.
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);
}
//count==0
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);
} |
