public String(char value[], int offset, int count) {
if (offset < 0) {
throw new StringIndexOutOfBoundsException(offset);
}
if (count < 0) {
throw new StringIndexOutOfBoundsException(count);
}
// Note: offset or count might be near -1>>>1.
if (offset > value.length - count) {
throw new StringIndexOutOfBoundsException(offset + count);
}
this.offset = 0;
this.count = count;
this.value = Arrays.copyOfRange(value, offset, offset+count);
}
构造String时首先看offset是否小于0，如果不是则实用数组的复制方式从第一位开始复制count位数据。
public boolean equals(Object anObject) {if (this == anObject) { return true; } if (anObject instanceof String) { String anotherString = (String)anObject; int n = count; if (n == anotherString.count) { char v1[] = value; char v2[] = anotherString.value; int i = offset; int j = anotherString.offset; while (n-- != 0) { if (v1[i++] != v2[j++]) return false; } return true; } } return false; }采用数组方式存储数据后逐个对比。
public int compareTo(String anotherString) {int len1 = count; int len2 = anotherString.count; int n = Math.min(len1, len2); char v1[] = value; char v2[] = anotherString.value; int i = offset; int j = anotherString.offset; if (i == j) { int k = i; int lim = n + i; while (k < lim) { char c1 = v1[k]; char c2 = v2[k]; if (c1 != c2) { return c1 - c2; } k++; } } else { while (n-- != 0) { char c1 = v1[i++]; char c2 = v2[j++]; if (c1 != c2) { return c1 - c2; } } } return len1 - len2; }采用数组方式存储后逐个对比，不同的用ascii码标记。 public int hashCode() {int h = hash; if (h == 0 && count > 0) { int off = offset; char val[] = value; int len = count; for (int i = 0; i < len; i++) { h = 31*h + val[off++]; } hash = h; } return h; }用31为计算因子。 public int indexOf(int ch, int fromIndex) {if (fromIndex < 0) { fromIndex = 0; } else if (fromIndex >= count) { // Note: fromIndex might be near -1>>>1. return -1; } if (ch < Character.MIN_SUPPLEMENTARY_CODE_POINT) { // handle most cases here (ch is a BMP code point or a // negative value (invalid code point)) final char[] value = this.value; final int offset = this.offset; final int max = offset + count; for (int i = offset + fromIndex; i < max ; i++) { if (value[i] == ch) { return i - offset; } } return -1; } else { return indexOfSupplementary(ch, fromIndex); } }用数组存储后获取指定字符。