Integer.valueOf与Integer.parseInt的小疑惑

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

    */



}