【Java】创建对象的几种方式

1.new创建新的对象

String str = new String("str");

2.通过Java的反射机制

public static void main(String[] args) throws Exception {
        // 获取类的Class对象
       String str = (String)Class.forName("java.lang.String").newInstance();

　　　　System.out.println(str); 
 }

3.通过clone机制(克隆机制)

=========================Myclass.java===========================================
public class MyClass implements Cloneable {
    private int value;

    public MyClass(int value) {
        this.value = value;
    }

    public int getValue() {
        return value;
    }

    @Override
    public MyClass clone() throws CloneNotSupportedException {
        return (MyClass) super.clone();
    }
}
===========================Main.java=============================================
public class Main {
    public static void main(String[] args) throws CloneNotSupportedException {
        MyClass obj1 = new MyClass(10);
        MyClass obj2 = obj1.clone();

        System.out.println(obj1.getValue()); // 输出：10
        System.out.println(obj2.getValue()); // 输出：10
    }
}

4.通过序列化机制

　　通过序列化机制来创建新的对象。序列化是将对象转换为字节流的过程，以便可以将其存储在磁盘上或通过网络传输。反序列化则是将字节流转换回对象的过程。

===================================================================================================

import java.io.*;

public class MyClass implements Serializable {
    private int value;

    public MyClass(int value) {
        this.value = value;
    }

    public int getValue() {
        return value;
    }

    private void writeObject(ObjectOutputStream out) throws IOException {
        out.writeInt(value * 2);
    }

    private void readObject(ObjectInputStream in) throws IOException, ClassNotFoundException {
        value = in.readInt();
    }
}
===================================================================================================
public class Main {
    public static void main(String[] args) throws IOException, ClassNotFoundException {
        MyClass obj1 = new MyClass(10);
        FileOutputStream fileOut = new FileOutputStream("obj1.ser");
        ObjectOutputStream out = new ObjectOutputStream(fileOut);
        out.writeObject(obj1);
        out.close();
        fileOut.close();

        FileInputStream fileIn = new FileInputStream("obj1.ser");
        ObjectInputStream in = new ObjectInputStream(fileIn);
        MyClass obj2 = (MyClass) in.readObject();
        in.close();
        fileIn.close();

        System.out.println(obj1.getValue()); // 输出：10
        System.out.println(obj2.getValue()); // 输出：20
    }
}

 

5、构造函数对象的newInstance()方法

类Constructor也有newInstance方法，这一点和Class有点像。从它的名字可以看出它与Class的不同，Class是通过类来创建对象，而Constructor则是通过构造器。依然使用第一个例子中的Test类。

public static void main(String[] args) throws Exception {
    Constructor<Test> constructor;
   try {
        constructor = Test.class.getConstructor();
       Test t = constructor.newInstance();
   } catch (InstantiationException |
        IllegalAccessException |
        IllegalArgumentException |
        InvocationTargetException |
        NoSuchMethodException |
        SecurityException e) {
        e.printStackTrace();
   }
}