从Zero学习String源码

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源码版本：JDK_1.7.0_55

String的常用方法

public final class String  //注意final    implements java.io.Serializable, Comparable<String>, CharSequence {    //保证只能初始化一次，用字符数组来存    private final char value[];    // 存储hashCode，默认为0    private int hash;     //判断是否相等    public boolean equals(Object anObject) {        if (this == anObject) {  //同一对象            return true;        }        if (anObject instanceof String) { //若同为String类型            String anotherString = (String) anObject;            int n = value.length;  //本字符串长度            if (n == anotherString.value.length) { //长度相同，比较每个字符（ASCII码）是否相同                char v1[] = value;                char v2[] = anotherString.value;                int i = 0;                while (n-- != 0) {                    if (v1[i] != v2[i])                            return false;                    i++;                }                return true;  //相等返回            }        }        return false;    }    //比较String的大小，返回的是 "str1 - str2"    public int compareTo(String anotherString) {        int len1 = value.length;        int len2 = anotherString.value.length;        int lim = Math.min(len1, len2);  //得到小的长度（可以比较的最大长度）        char v1[] = value;        char v2[] = anotherString.value;        int k = 0;          while (k < lim) {  //从0比较到lim-1            char c1 = v1[k];            char c2 = v2[k];            if (c1 != c2) {                return c1 - c2; //不相等返回            }            k++;        }        return len1 - len2;  //若v[lim-1]以前都相等,则判断长度，长的值大    }    //获得hashCode，赋值给hash    public int hashCode() {        int h = hash;        if (h == 0 && value.length > 0) {         //若之前没有计算过hashCode，且存在String，则生成一个hashCode            char val[] = value;            for (int i = 0; i < value.length; i++) {                h = 31 * h + val[i];  //计算方法，为了唯一性.            }            hash = h;        }        return h;    }    /*看了下"zero"生成hashCode过程：        0:122        1:3883        2:120487        3:3735208        hashCode:3735208    */    //得到某一字符    public char charAt(int index) {        if ((index < 0) || (index >= value.length)) { //是否越界            throw new StringIndexOutOfBoundsException(index);        }        return value[index]; //直接下标返回    }    //替换方法    public String replace(char oldChar, char newChar) {        if (oldChar != newChar) {            int len = value.length;            int i = -1;            char[] val = value; /* avoid getfield opcode */            while (++i < len) {                if (val[i] == oldChar) { //遍历判断第一个oldChar的位置                    break;                }            }            if (i < len) { //存在oldChar                char buf[] = new char[len]; //重新生成等长字符数组                for (int j = 0; j < i; j++) {                    buf[j] = val[j];  //0至i-1的值保持不变                }                while (i < len) {                    char c = val[i];                    buf[i] = (c == oldChar) ? newChar : c;                     //找到存在oldChar位置的地方，在新字符数组处赋值为newChar；                    i++;                }                return new String(buf, true);  //实际上是重新生成了一个String            }        }        return this;    }    //去掉两端的空格    public String trim() {        int len = value.length;        int st = 0;        char[] val = value;    /* avoid getfield opcode */        while ((st < len) && (val[st] <= ' ')) {  //从前往后判断            st++;        }        while ((st < len) && (val[len - 1] <= ' ')) { //后往前            len--;        }        return ((st > 0) || (len < value.length)) ? substring(st, len) : this;        //substring(st, len),里面是用了Arrays里面的copyOfRange方法        /*        public static char[] copyOfRange(char[] original, int from, int to) {            int newLength = to - from;            if (newLength < 0)                throw new IllegalArgumentException(from + " > " + to);            char[] copy = new char[newLength];            //native方法               System.arraycopy(original, from, copy, 0,                               Math.min(original.length - from, newLength));            return copy;        }        */    }    public native String intern();     ...}