//源码
public final class Integer extends Number implements Comparable<Integer>

    //源码/*** A constant holding the minimum value an {@code int} can* have, -2<sup>31</sup>.*/@Native public static final int   MIN_VALUE = 0x80000000;/*** A constant holding the maximum value an {@code int} can* have, 2<sup>31</sup>-1.*/@Native public static final int   MAX_VALUE = 0x7fffffff;

    //源码public Integer(int value) {this.value = value;}public Integer(String s) throws NumberFormatException {this.value = parseInt(s, 10);}

     parseInt("0", 10) returns 0parseInt("473", 10) returns 473parseInt("+42", 10) returns 42parseInt("-0", 10) returns 0parseInt("-FF", 16) returns -255parseInt("1100110", 2) returns 102parseInt("2147483647", 10) returns 2147483647parseInt("-2147483648", 10) returns -2147483648parseInt("2147483648", 10) throws a NumberFormatExceptionparseInt("99", 8) throws a NumberFormatExceptionparseInt("Kona", 10) throws a NumberFormatExceptionparseInt("Kona", 27) returns 411787

　　//源码，限于篇幅简化了源码格式。public static int parseInt(String s, int radix) throws NumberFormatException {//这里有这个警告是因为valueOf方法使用了parseInt方法和IntegerCache对象，//因为valueOf在IntegerCache初始化之前使用导致异常情况。后面会详细分析。/** WARNING: This method may be invoked early during VM initialization* before IntegerCache is initialized. Care must be taken to not use* the valueOf method.*///下面三个if用来判断参数是否合法。radix大小在2~36之间。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; //解析结果boolean negative = false; //是否是负数int i = 0, len = s.length(); //索引变量和字符串长度int limit = -Integer.MAX_VALUE; //最大值限制int multmin; //基数下的最小值int digit; //记录每一位的数字if (len > 0) {char firstChar = s.charAt(0);if (firstChar < '0') { // 判断是否带‘+’或‘-’if (firstChar == '-') {negative = true;limit = Integer.MIN_VALUE;} else if (firstChar != '+')throw NumberFormatException.forInputString(s);if (len == 1) // 格式非法，含有除了‘+’‘-’之外的字符。throw NumberFormatException.forInputString(s);i++;}multmin = limit / radix;while (i < len) {//利用了Character类中的digit非法，作用是解析一个字符。digit = Character.digit(s.charAt(i++),radix);//进行异常判断。//这个解析字符串为数字的算法和平时想到的不太一样，是从字符串左边开始，初始化结果是0，//其实是把结果算成负的，返回的时候再转回来。result -= digit;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);}return negative ? result : -result; //如果是负的就直接返回，因为算出来的已经是负数。}

　　//源码    public static int parseInt(String s) throws NumberFormatException {return parseInt(s,10);}

//源码public static Integer valueOf(String s, int radix) throws NumberFormatException {return Integer.valueOf(parseInt(s,radix));}
public static Integer valueOf(String s) throws NumberFormatException {return Integer.valueOf(parseInt(s, 10));}

　　//源码　　public static Integer valueOf(int i) {if (i >= IntegerCache.low && i <= IntegerCache.high)return IntegerCache.cache[i + (-IntegerCache.low)];return new Integer(i);}

//源码
private static class IntegerCache {static final int low = -128; //默认low=-128static final int high; //high可以配置，通过 VM 参数-XX:AutoBoxCacheMax=<size>//high可以配置，所以默认缓存-128~127，但是也可以缓存另外的常用数。static final Integer cache[]; //缓存数组//静态代码块，Integer类加载时就缓存。static {// high value may be configured by propertyint h = 127; //默认127String integerCacheHighPropValue =sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high"); //读取VM参数配置。if (integerCacheHighPropValue != null) {try {int i = parseInt(integerCacheHighPropValue);i = Math.max(i, 127); //缓存大数// Maximum array size is Integer.MAX_VALUEh = Math.min(i, Integer.MAX_VALUE - (-low) -1); //防止越界} catch( NumberFormatException nfe) {// If the property cannot be parsed into an int, ignore it.
            }}high = h;cache = new Integer[(high - low) + 1]; //创建缓存数组。int j = low;for(int k = 0; k < cache.length; k++)cache[k] = new Integer(j++); //缓存。// range [-128, 127] must be interned (JLS7 5.1.7)assert IntegerCache.high >= 127; //保证[-128, 127]在缓存范围内。
    }private IntegerCache() {}
}

　　　　//首先要明确一点，对象之间的==是比较内存地址，常数之间的比较是数值比较。　　public static void main(String[] args) {Integer num1 = new Integer(100);Integer num2 = new Integer(100);System.out.println(num1 == num2);//false,因为这两个对象是独立创建的，有自己的内存空间和地址。Integer num3 = 100;Integer num4 = 100;System.out.println(num3 == num4);//true，常数之间比较数值。Integer num5 = 128;Integer num6 = 128;System.out.println(num5 == num6);//false，自动装箱成对象，但是超过了默认的缓存范围，同第一个。如果是127就是true。Integer num7 = 100;Integer num8 = new Integer(100);System.out.println(num7 == num8);//false，两个对象之间比较内存地址，不同的是num7通过自动装箱调用valueOf方法，指向缓存的100，而num8是指向自己内存空间里的100.int num9 = 100;Integer num10 = new Integer(100);　　　　 System.out.println(num9 == num10);//true，Integer对象和int比较时，Integer会自动拆箱（intValue方法）成为int，变成两个数值比较。Integer num11 = 100;System.out.println(num9 == num11);//true，num11通过自动装箱调用valueOf方法指向缓存中的100，比较的时候缓存中的100对象自动拆箱成为数值100.}