java achieve two ways serialized

1.Serializable Interface

2.Exteranalizable Interface

public class Demo2 implements Externalizable{

    transient private String s="sss";
    public int b=10;
    public String ss="iiii";
    public int a=1;
    
    @Override
    public void writeExternal(ObjectOutput out) throws IOException {
        out.writeObject(ss);
        out.writeObject(a);
    }
    @Override
    public void readExternal(ObjectInput in) throws IOException, ClassNotFoundException {
        ss =(String)in.readObject();
        a =(Integer)in.readObject();
    }
    @Override
    public String toString() {
        return "Demo2 [ss=" + ss + ", a=" + a + "]";
    }
}

测试：

public class Test {
    public static void main(String[] args) throws FileNotFoundException, IOException, ClassNotFoundException {
        
        Demo2 demo2=new Demo2();
        ObjectOutputStream oos=new ObjectOutputStream(new FileOutputStream("D:\\Desktop\\a.txt"));
        oos.writeObject(demo2);
        oos.close();
        
        ObjectInputStream ois=new ObjectInputStream(new FileInputStream("D:\\Desktop\\a.txt"));
        Object object = ois.readObject();
        System.out.println(object);        
        ois.close();
    }
}