Java String Source code in openjdk-7

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。