参考博客：

http://www.importnew.com/9162.html

 

测试代码如下：

public class Main {    /**     * 备注：结果跟你的JDK版本有关系：     *      * 我的是java version "1.6.0_16"     *      *这是JDK中的Integer.java中valueOf的源代码：      public static Integer valueOf(String s) throws NumberFormatException {        return Integer.valueOf(parseInt(s, 10));      }            public static Integer valueOf(int i) {        if(i >= -128 && i <= IntegerCache.high)            return IntegerCache.cache[i + 128];        else            return new Integer(i);     }           public static int parseInt(String s) throws NumberFormatException {        return parseInt(s,10);     }             public static int parseInt(String s, int radix)        throws NumberFormatException    {        if (s == null) {            throw new NumberFormatException("null");        }    if (radix < Character.MIN_RADIX) {        throw new NumberFormatException("radix " + radix +                        " less than Character.MIN_RADIX");    }    if (radix > Character.MAX_RADIX) {        throw new NumberFormatException("radix " + radix +                        " greater than Character.MAX_RADIX");    }    int result = 0;    boolean negative = false;    int i = 0, max = s.length();    int limit;    int multmin;    int digit;    if (max > 0) {        if (s.charAt(0) == '-') {        negative = true;        limit = Integer.MIN_VALUE;        i++;        } else {        limit = -Integer.MAX_VALUE;        }        multmin = limit / radix;        if (i < max) {        digit = Character.digit(s.charAt(i++),radix);        if (digit < 0) {            throw NumberFormatException.forInputString(s);        } else {            result = -digit;        }        }        while (i < max) {        // Accumulating negatively avoids surprises near MAX_VALUE        digit = Character.digit(s.charAt(i++),radix);        if (digit < 0) {            throw NumberFormatException.forInputString(s);        }        if (result < multmin) {            throw NumberFormatException.forInputString(s);        }        result *= radix;        if (result < limit + digit) {            throw NumberFormatException.forInputString(s);        }        result -= digit;        }    } else {        throw NumberFormatException.forInputString(s);    }    if (negative) {        if (i > 1) {        return result;        } else {            throw NumberFormatException.forInputString(s);        }    } else {        return -result;    }    }     * @param args     */    public static void main(String[] args) {        System.out.println(Integer.valueOf(127) == Integer.valueOf(127));        System.out.println(Integer.valueOf("127") == Integer.valueOf(127));        System.out.println(Integer.valueOf("127") == Integer.valueOf("127"));                System.out.println(Integer.parseInt("127") == Integer.parseInt("127"));                System.out.println(Integer.valueOf(127) == Integer.parseInt("127"));        System.out.println(Integer.valueOf("127") == Integer.parseInt("127"));        System.out.println(Integer.valueOf(128) == Integer.valueOf(128));        System.out.println(Integer.valueOf("128") == Integer.valueOf(128));        System.out.println(Integer.valueOf("128") == Integer.valueOf("128"));        System.out.println(Integer.parseInt("128") == Integer.parseInt("128"));                System.out.println(Integer.valueOf(128) == Integer.parseInt("128"));        System.out.println(Integer.valueOf("128") == Integer.parseInt("128"));                    }    /**    true    true    true    true    true    true    false    false    false    true    true    true    */}