private final char value[];

   private int hash; // Default to 0

 public String(String original) {

        this.value = original.value;

        this.hash = original.hash;

    }

 public String(char value[]) {

        this.value = Arrays.copyOf(value, value.length);

    }

String：

 |--CompareTo

 public int compareTo(String anotherString) {

        int len1 = value.length;

        int len2 = anotherString.value.length;

        int lim = Math.min(len1, len2);         //取较小长度的字符串作为比较长度

        char v1[] = value;

        char v2[] = anotherString.value;

        int k = 0;

        while (k < lim) {

            char c1 = v1[k];

            char c2 = v2[k];

            if (c1 != c2) {                    //逐个比较

                return c1 - c2;

            }

            k++;

        }

        return len1 - len2;

    }

|--equals

 public boolean equals(Object anObject) {

        if (this == anObject) {           //地址相同直接判断相等

            return true;

        }

        if (anObject instanceof String) {  //先判别类是否相同

            String anotherString = (String)anObject;

            int n = value.length;

            if (n == anotherString.value.length) {  //字符串长度是否一致

                char v1[] = value;

                char v2[] = anotherString.value;

                int i = 0;

                while (n-- != 0) {

                    if (v1[i] != v2[i])           //逐个进行比较

                        return false;

                    i++;

                }

                return true;

            }

        }

        return false;

    }  

|--hashCode

 public int hashCode() {

        int h = hash;

        if (h == 0 && value.length > 0) {

            char val[] = value;

            for (int i = 0; i < value.length; i++) {

                h = 31 * h + val[i];

            }

            hash = h;

        }

        return h;

    }

 //toString的经典实现

     public static String toString(int[] a) {

            if (a == null)

                return "null";

            int iMax = a.length - 1;

            if (iMax == -1)

                return "[]";

            StringBuilder b = new StringBuilder();

            b.append('[');

            for (int i = 0; ; i++) {//中间省略判断，提高效率

                b.append(a[i]);

                if (i == iMax)

                    return b.append(']').toString();

                b.append(", ");

            }

        }