JAVA創建對象的幾種方式

  四種創建對象的方法

　　一, new

　　二, clone()

　　三, 對象序列化

　　四, reflect

package com.nemo.clone;

import java.io.Serializable;

public class Clerk implements Serializable{
    private int id;
    private String name;
    
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    
}

package com.nemo.clone;

import java.io.Serializable;

public class Company implements Serializable,Cloneable{
    private String name;
    private Clerk clerk;
    
    public Company(String name,Clerk clerk) {
        this.name = name;
        this.clerk = clerk;
    }
    
    public Company() {
        
    }
    
    @Override
    public Object clone() throws CloneNotSupportedException {
        return super.clone();
    }
    
    public void dynamicParameter(String ...strings ) {
        for(String x : strings) {
            System.out.println(x);
        }
    }
    
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public Clerk getClerk() {
        return clerk;
    }
    public void setClerk(Clerk clerk) {
        this.clerk = clerk;
    }
}

 

第二種在"深拷貝和淺拷貝"已經實現過了。

 

第三種對象序列化

public static void createObjectBySerializable() throws IOException, ClassNotFoundException {
        Clerk clerk = new Clerk();
        clerk.setId(123);
        clerk.setName("xxx");

        Company company = new Company();
        company.setName("nmt");
        company.setClerk(clerk);

        OutputStream fileOutputStream = new FileOutputStream("bak.tmp");
        ObjectOutputStream outputStream = new ObjectOutputStream(fileOutputStream);
        outputStream.writeObject(company);

        InputStream fileInputStream = new FileInputStream("bak.tmp");
        ObjectInputStream inputStream = new ObjectInputStream(fileInputStream);

        Company scompany = (Company) inputStream.readObject();
        System.out.println(company);
        System.out.println(company.getClerk());
        company.setName("company one");
        company.getClerk().setId(888);
        company.getClerk().setName("xxx");

        System.out.println(scompany);
        System.out.println(scompany.getClerk());
        scompany.getClerk().setId(999);
        scompany.getClerk().setName("yyy");
        scompany.setName("company two");

        System.out.println(company.getName());
        System.out.println(company.getClerk().getId());
        System.out.println(company.getClerk().getName());
        System.out.println("----------------------------");
        System.out.println(scompany.getName());
        System.out.println(scompany.getClerk().getId());
        System.out.println(scompany.getClerk().getName());
    }

com.nemo.clone.Company@173a10f
com.nemo.clone.Clerk@530daa
com.nemo.clone.Company@de6f34
com.nemo.clone.Clerk@156ee8e
company one
888
xxx
----------------------------
company two
999
yyy

 注意點 : 被創建的對象必須要實現Serializable接口

 這種方式的創建對象和深拷貝的結果是一樣的。 對象內的引用類型也會復制一份而不是共享。

 

第四種 reflect 

public static void createObjectByReflect() throws SecurityException, NoSuchMethodException,
            IllegalArgumentException, InstantiationException, IllegalAccessException,
            InvocationTargetException {
        
        Class clazz = Company.class;
        Constructor con = clazz .getConstructor(String.class,Clerk.class);
        Company company = (Company) con.newInstance("xxx",new Clerk());
        
        Method method = clazz.getMethod("dynamicParameter",(new String[]{}.getClass()));
        method.invoke(company, (Object)new String[]{"xxx"});
        
        System.out.println(company);
        System.out.println(company.getName());
        
    }

使用class對象獲取此類的構造器,然后使用構造器的newInstance()方法創建一個對象。

 

 

(遇到一個問題,這里在使用反射調用變長參數的方法時,入參會有點不同。

method.invoke(company, (Object)new String[]{"xxx"}); 必須使用(Object)強制轉換。 如果直接用String[]則會報錯。)