Java自动装箱与拆箱
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// Copyright (c) 1998-1998 GEMALTO group. All Rights Reserved.
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// This software is the confidential and proprietary information of
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// Project name: CSTK
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// Platform : Java virtual machine
// Language : JAVA 1.6.0
// Devl tool : Eclipse
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// Workfile
// version: 1.0
// Date : 2009-7-17
// Author :
// Modtime:
//
// Original author:
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//-------------------------------------------------------------------------
package org.zdxue.javase.lang;
/**
* Java自动装箱与拆箱
*
* @version 1.0 - 2009-7-17
* @author
*/
public class Boxing_Unboxing
{
public static void main(String[] args)
{
Integer a = 1024; //自动装箱(编辑器会隐式处理为：Integer a = new Integer(1024); )
Integer b = 1024; //自动装箱(编辑器会隐式处理为：Integer b = new Integer(1024); )
int c = 1024; //基本数据类型
int d = a; //自动拆箱(编辑器会隐式处理为：int d = a.intValue(); )
double e = a;//自动拆箱(编辑器会隐式处理为：int d = a.doubleValue(); )
short f = a.shortValue(); //不可以写成：short f = a; 因为隐式转换会丢失精度，必须向上（高精度）转型
boolean test = a < b || a == b || a > b; //对象运算
System.out.println(test);
System.out.println(a == c); //自动将a拆箱后，与c进行计算
System.out.println(d);
System.out.println(e);
System.out.println(d == e);
System.out.println(f);
//---------------------------------------------
/**
* int值在-128~127之间，装箱时，在内存堆中只new一次，则h1,h2指向同一个对象，因此地址== true
* 但是不在上述的范围时（-128~127），会在内存堆中各个new一次，也就是说，引用地址是不同的，因此== false
*/
Integer h1 = 127;
Integer h2 = 127;
System.out.println("h1=h2 ->" + (h1 == h2)); //在范围内，true
Integer h3 = 128;
Integer h4 = 128;
System.out.println("h3=h4 ->" + (h3 == h4)); //不在范围内，false
//--------------------------------------
Long l1 = 128L;
Long l3 = 128L;
long l2 = 100;
Long l5 = 127L;
Long l4 = 127L;
System.out.println("l1==l2 -> " + (l1 == l2));
System.out.println("l1==l3 -> " + (l1 == l3)); //不在范围内，false
System.out.println("l4==l5 -> " + (l4 == l5)); //在范围内(-128~127)，true
//---------------- 注意 ------------------------------------
Integer i = null;
//int j = i.intValue();
int j = i; //编译上没有问题，但是已经隐含NullPointerException, 编译器会处理为：ing j = i.intValue();
System.out.println(j);
//---------------------------------------------------------
int d0 = 100;
Double d1 = (double)d0; //注意与下面的区别
double d2 = d0;
}
}