String类型中ToString hashCode equals compareTo等方法的经典实现

   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(", ");
            }
        }