String類有兩個私有的變量，字符數組value，和整型變量hash(默認為0)。

1     /** The value is used for character storage. */
2     private final char value[];
3 
4     /** Cache the hash code for the string */
5     private int hash; // Default to 0

下面對一些常用方法進行分析。

length()

 1  /**
 2      * Returns the length of this string.
 
 3      * The length is equal to the number of <a href="Character.html#unicode">Unicode
 4      * code units</a> in the string.
 5      *
 6      * @return  the length of the sequence of characters represented by this
 7      *          object.
 8      */
 9     public int length() {
 
10         return value.length;
11     }

、isEmpty()、charAt(int index)、equals(Object anObject)、hashCode()、indexOf(int ch)、substring(int beginIndex)、concat(String str)、

replace(char oldChar, char newChar) 、contains(CharSequence s)、

JDK源碼閱讀(1.8) —— String