java Integer 思考题

 

 

public static void main(String[] args) {
Integer i1 = new Integer(97);
Integer i2 = new Integer(97);
System.out.println(i1 == i2); //false
System.out.println(i1.equals(i2)); //true
System.out.println("-----------");

Integer i3 = new Integer(197);
Integer i4 = new Integer(197);
System.out.println(i3 == i4); //false
System.out.println(i3.equals(i4)); //true
System.out.println("-----------");

Integer i5 = 127;
Integer i6 = 127;
System.out.println(i5 == i6); //true
System.out.println(i5.equals(i6)); //true
System.out.println("-----------");

Integer i7 = 128;
Integer i8 = 128;
System.out.println(i7 == i8);
System.out.println(i7.equals(i8)); //true


* -128到127是byte的取值范围,如果在这个取值范围内,自动装箱就不会新创建对象,而是从常量池中获取
* 如果超过了byte取值范围就会再新创建对象
*
* public static Integer valueOf(int i) {   //     Integer  valueof 源码
assert IntegerCache.high >= 127;
if (i >= IntegerCache.low && i <= IntegerCache.high) //i>= -128 && i <= 127
return IntegerCache.cache[i + (-IntegerCache.low)];          //创建数组
return new Integer(i);
}
*/
}