java String源码学习

public final class Stringimplements java.io.Serializable, Comparable<String>, CharSequence {/**char数组用于字符的存储 */private final char value[];/** 缓存string的hash码 */private int hash; // Default to 0public String() {/**无参构造函数,打印值为""*/this.value = new char[0];}public String(String original) {/**字符值和hash值均为参数的值*/
this.value = original.value;this.hash = original.hash;}public String(char value[]) {/**Arrays.copyOf()方法返回一个新构造的
char数组*/this.value = Arrays.copyOf(value, value.length);}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.value = Arrays.copyOfRange(value, offset, offset+count);}/**传入代码点来构造String对象,代码点和代码单元相关内容可自行查阅资料,或者看我另一篇随笔深入学习Java中的字符串,代码点和代码单元*/

public String(int[] codePoints, 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 > codePoints.length - count) {throw new StringIndexOutOfBoundsException(offset + count);}final int end = offset + count;/**计算char数组的真实大小,一个代码点有可能需要用2个char即2个代码单元表示*/int n = count;for (int i = offset; i < end; i++) {int c = codePoints[i];if (Character.isBmpCodePoint(c))/**此代码点为基本字符代码点*/continue;else if (Character.isValidCodePoint(c))/**此代码点为有效代码点,即辅助字符代码点,此时一个代码点需要用2个char即2个代码单元表示,n++*/n++;else throw new IllegalArgumentException(Integer.toString(c));}/**分配并填充字符数组*/final char[] v = new char[n];for (int i = offset, j = 0; i < end; i++, j++) {int c = codePoints[i];if (Character.isBmpCodePoint(c))v[j] = (char)c;elseCharacter.toSurrogates(c, v, j++);}this.value = v;}/**返回指定下标的字符*/public char charAt(int index) {if ((index < 0) || (index >= value.length)) {throw new StringIndexOutOfBoundsException(index);}return value[index];}/**返回指定下标的代码点*/
public int codePointAt(int index) {if ((index < 0) || (index >= value.length)) {throw new StringIndexOutOfBoundsException(index);}return Character.codePointAtImpl(value, index, value.length);}public boolean equals(Object anObject) {if (this == anObject) {return true;/**如果是同一个对象,直接返回true*/}if (anObject instanceof String) {String anotherString = (String) anObject;int n = value.length;if (n == anotherString.value.length) {char v1[] = value;char v2[] = anotherString.value;int i = 0;while (n-- != 0) {if (v1[i] != v2[i])return false;i++;}return true;}}return false;}public boolean contentEquals(StringBuffer sb) {synchronized (sb) {/**锁定StringBuffer对象,防止修改*/return contentEquals((CharSequence) sb);}}public boolean equalsIgnoreCase(String anotherString) {return (this == anotherString) ? true: (anotherString != null)&& (anotherString.value.length == value.length)&& regionMatches(true, 0, anotherString, 0, value.length);}/**计算并返回hsah码*/
public int hashCode() {int h = hash;/**默认是0*/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;}/**字串为新对象*/
public String substring(int beginIndex) {if (beginIndex < 0) {throw new StringIndexOutOfBoundsException(beginIndex);}int subLen = value.length - beginIndex;if (subLen < 0) {throw new StringIndexOutOfBoundsException(subLen);}return (beginIndex == 0) ? this : new String(value, beginIndex, subLen);}
/**连接字符串*/
public String concat(String str) {int otherLen = str.length();if (otherLen == 0) {return this;}int len = value.length;char buf[] = Arrays.copyOf(value, len + otherLen);str.getChars(buf, len);/**将str内的字符依次存放到buf数组中,下标从len开始*/return new String(buf, true);/**返回新生成的对象*/}/**trim()方法将字符串首尾的ascii码数值小于或等于空格的字符删除*/
public String trim() {int len = value.length;int st = 0;char[] val = value;    /* avoid getfield opcode */while ((st < len) && (val[st] <= ' ')) {/**从字符串首个字符开始判断ascii是否小于或等于空格,若小于或等于,计数++*/st++;}while ((st < len) && (val[len - 1] <= ' ')) {/**从字符串最后一个字符开始判断ascii是否小于或等于空格,若小于或等于,计数--*len--;}return ((st > 0) || (len < value.length)) ? substring(st, len) : this;}/**返回自身对象的引用*/
public String toString() {return this;}/**和toString()唯一区别就是先判断对象是否为空*/
public static String valueOf(Object obj) {return (obj == null) ? "null" : obj.toString();}