1.什么是自动装箱与自动拆箱?
Demo:
Integer int1 = 100;
Integer int2 = 100;
Integer int3 = 200;
Integer int4 = 200;
System.out.println(int1==int2);//true
System.out.println(int3==int4);//false
//自动装箱
Integer int1 = 100;
//自动拆箱
int int2 = int1;
简单点说,装箱就是自动将基本数据类型转换为包装类型;拆箱就是自动将包装类型转换为基本数据类型。八种基本数据类型都可进行自动装箱:
public final class Integer extends Number implements Comparable<Integer> {
private final int value;
public Integer(int value) {
this.value = value;
}
public Integer(String s) throws NumberFormatException {
this.value = parseInt(s, 10);
}
}
public static Integer valueOf(int i) {
if (i >= IntegerCache.low && i <= IntegerCache.high)
return IntegerCache.cache[i + (-IntegerCache.low)];
//上述代码可以简化如下
//if (i >= -128 && i <= 127)
// return IntegerCache.cache[i + 128];
return new Integer(i);
}