Java实例化类的方法
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下一篇 2012-05-25 09:06:42
/ 个人分类:Java
Java中,类的实例化方法有四种途径:%w-?_emzc0 1)使用new操作符51Testing软件测试网 l%rHlJg ~(~%d
` bU7c8up:I]X6v8s0 2)调用Class对象的newInstance()方法
TtJm%j+W|0tj6NO^f5q0 3)调用clone()方法,对现有实例的拷贝51Testing软件测试网-x\,~ D,s6TW(b:F}
51Testing软件测试网;Z/|x_8? 4)通过ObjectInputStream的readObject()方法反序列化类
`Eqwht8QY {051Testing软件测试网i8~S+nzS/x[ 1、ClassInstance.java
F!Yt qBo(l)Rt0- import java.io.*;
-
- class ClassInstance implements Cloneable, Serializable {
- private String str = "测试...";
- public void fun(){
- System.out.println(str);
- }
- public ClassInstance(String str){
- System.out.println("有参类的实例化");
- this.str += str;
- }
- public ClassInstance(){
- System.out.println("无参类的实例化");
- }
- public Object clone(){
- return this;
- }
- }
|
5U7zK2g{DtQB^0 2、ClassInstanceTest.java51Testing软件测试网a3t,u#j(i
dz]
- import java.io.*;
- import java.lang.reflect.*;
-
- public class ClassInstanceTest{
- public static void main(String[] args) throws ClassNotFoundException, InstantiationException,
- IllegalAccessException, IOException,InvocationTargetException, NoSuchMethodException{
-
- ClassInstance ci01 = new ClassInstance("01");
- ci01.fun();
-
-
- ClassInstance ci02 = (ClassInstance) Class.forName("ClassInstance").newInstance();
- ci02.fun();
-
-
- ClassInstance ci03 = (ClassInstance) ci01.clone();
- ci03.fun();
-
-
- FileOutputStream fos = new FileOutputStream("ci.tmp");
- ObjectOutputStream oos = new ObjectOutputStream(fos);
- oos.writeObject(ci01);
- oos.close();
- fos.close();
-
- FileInputStream fis = new FileInputStream("ci.tmp");
- ObjectInputStream ois = new ObjectInputStream(fis);
-
- ClassInstance ci04 = (ClassInstance) ois.readObject();
- ois.close();
- fis.close();
-
- ci04.fun();
- System.out.println("--------------------额外测试--------------------");
- ClassInstance ci05 = null;
-
-
- Constructor[] ctor = Class.forName("ClassInstance").getDeclaredConstructors();
-
- for(int i=0;i<ctor.length;i++ ){
- Class[] cl = ctor[i].getParameterTypes();
- if(cl.length == 1){
-
- ci05 = (ClassInstance) Class.forName("ClassInstance").getConstructor(cl).newInstance(new Object[]{"05"});
- }
- }
- ci05.fun();
- }
- }
|
yOcQAS#F0 3、输出结果51Testing软件测试网z)y8Z/l'LkS
- 有参类的实例化
- 测试...01
- 无参类的实例化
- 测试...
- 测试...01
- 测试...01
- -------------------额外测试--------------------
- 有参类的实例化
- 测试...05
|
51Testing软件测试网1k;[XH4qBYd7H(m 除了这几种情况可以实例化一个Java类对象外,隐式调用实例化也是利用了已上集中情况。例如常见的方法:
[9G?4q3HnAeT0Ea0- public class ClassInstance{
- public ClassInstance(){
- }
- public ClassInstance getInstance(){
- return new ClassInstance();
- }
- }
|
6?3oU2E!M@0 通过观察结果,我们发现无论哪一种方式必须经过的一步---调用构造方法。无论怎样构造函数作为初始化类的意义怎样都不会改变。
pV/z%~\|[J,]l0
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