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java 创建对象的四种方法

2019-05-24

java 创建对象的四种方法

java 四种方法创建对象
Java 中创建对象的四种方式

(1) 用 new 语句创建对象，这是最常见的创建对象的方法。
(2) 运用反射手段,调用 java.lang.Class 或者 java.lang.reflect.Constructor 类的 newInstance()实例方法。
(3) 调用对象的 clone()方法。
(4) 运用反序列化手段，调用 java.io.ObjectInputStream 对象的 readObject()方法。

一.用 new 语句创建对象
Java 代码
User user = new User()

二.运用反射手段
(1)调用 java.lang.Class.newInstance()
Java 代码
Class.forName(classname).newInstance()
Wife wife = (Wife) Class.forName(“com.java.clone.Wife”).newInstance();

(2)调用 java.lang.reflect.Constructor 类的 newInstance()
Java 代码
Constructor constructor = Wife.class.getDeclaredConstructor(int.class,String.class);
Wife wife = (Wife) constructor.newInstance(1,”nihao”);

三.调用对象的 clone()方法
详情参考：http://ncs123.iteye.com/blog/1775631

Java 代码
Wife wife = new Wife(1,”wang”);
Wife wife2 = null;
wife2 = (Wife) wife.clone();//运用 clone()方法产生新对象

四.运用反序列化手段
被序列化的对象必须 implements Serializable

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public class BeanUtil {

    @SuppressWarnings("unchecked")
    public static <T> T cloneTo(T src) throws RuntimeException {
        ByteArrayOutputStream memoryBuffer = new ByteArrayOutputStream();
        ObjectOutputStream out = null;
        ObjectInputStream in = null;
        T dist = null;

        try {
            out = new ObjectOutputStream(memoryBuffer);
            out.writeObject(src);
            out.flush();
            in = new ObjectInputStream(new ByteArrayInputStream(
                    memoryBuffer.toByteArray()));
            dist = (T) in.readObject();

        } catch (Exception e) {
            throw new RuntimeException(e);
        } finally {
            if (out != null)
                try {
                    out.close();
                    out = null;
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
            if (in != null)
                try {
                    in.close();
                    in = null;
                } catch (IOException e) {
                    throw new RuntimeException(e);
                }
        }

        return dist;
    }

    public static void main(String[] args){
        Husband husband = new Husband(1);
        Wife wife = new Wife(1,"jin");
        husband.setWife(wife);
        Husband husband2 = cloneTo(husband);//运用反序列生成了一个对象
    }
}
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