new Integer() 与 Integer.valueOf() 的区别
1.首先先举一个例子
Integer a = new Integer(111);
Integer b = new Integer(111);
System.out.println(a == b); // false
Integer m = Integer.valueOf(111);
Integer n = Integer.valueOf(111);
System.out.println(m == n); // true
解释：new Integer()与Integer.valueOf()的区别在于：new Interger()每次都会创建一个对象；而Integer.valueOf()则是使用缓冲池中的对象，多次调用会取得同一个对象的引用；
缓冲池
以 Integer x = Integer.valueOf(123); 为例，首先先判断缓冲池中是否有当前数据，有就从InegerCache的缓存cache[] 数组中取出并返回，不同包装类的 cache[] 范围不同。
一些基本数据类型缓冲池的范围
boolean: true and false
short : between -128 and 127
int :between -128 and 127
char in the range \u0000 to \u007F
valueOf() 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);
}
IntegerCache源码
private static class IntegerCache {static final int low = -128;static final int high;static final Integer cache[];static {// high value may be configured by propertyint h = 127;String integerCacheHighPropValue =sun.misc.VM.getSavedProperty("java.lang.Integer.IntegerCache.high");if (integerCacheHighPropValue != null) {try {int i = parseInt(integerCacheHighPropValue);i = Math.max(i, 127);// Maximum array size is Integer.MAX_VALUEh = Math.min(i, Integer.MAX_VALUE - (-low) -1);} catch( NumberFormatException nfe) {// If the property cannot be parsed into an int, ignore it.}}high = h;cache = new Integer[(high - low) + 1];int j = low;for(int k = 0; k < cache.length; k++)cache[k] = new Integer(j++);// range [-128, 127] must be interned (JLS7 5.1.7)assert IntegerCache.high >= 127;}private IntegerCache() {}}