Java产生Class类的三种实例化对象的方法

Java产生Class类的三种实例化对象的方法

1.object.getClass
2.类名.class直接根据某个具体的类来取得Class实例化对象
3.Class.forName(String className)

public class TestClass {
    public static void main(String[] args) {
        //1.object.getClass
        Date date1 = new Date();
        Class cls = date1.getClass();

        //java.util.Date
        System.out.println("方法1 " + cls.getName());
        //class java.util.Date
        System.out.println("方法1 " + cls);

        //2.类名.class
        //一般用类的全限定名
        Class cls1 = java.util.Date.class;
        //class java.util.Date
        System.out.println("方法2 " + cls1);

        //3.推荐用
        Class cls2 = null;//放在外面可以访问
        try {
             cls2 = Class.forName("java.util.Date");
            System.out.println("方法3 " + cls2);
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
        System.out.println("比较三个对象");
        System.out.println(cls1 == cls);
        System.out.println(cls == cls2);
    }
}

推荐用第三种，第一种已经new了一个对象了，第二种写的太繁琐了

对象实例化的三种方法

1.new关键字Student student = new Student();
2.反射
（1）Class类的newInstance方法，也是基于Constructor类
（2）java.lang.relect.Constructor类的newInstance方法

public class TestClass1 {
    public static void main(String[] args) throws ClassNotFoundException, IllegalAccessException, InstantiationException {
        //1.getClass()方法
        Date date = new Date();
        Class cls = date.getClass();
        try {
            Date date1 = (Date) cls.newInstance();
            System.out.println("1 " + date1);
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        //2.全限定类名.class
        Class<java.util.Date> cls2 = java.util.Date.class;
        try {
            Date date3 = cls2.newInstance();
            System.out.println("2 "+date3);
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }

        Date date3 = cls2.newInstance();
        System.out.println("2 "+date3);
        //3.Class.forName方法，大写Class
        Class cls1 = Class.forName("java.util.Date");
        Object date2 = cls1.newInstance();
        System.out.println("3 " + date2);
    }
}

以上三种简单写法
1. Student student2 = (Student)Class.forName("Student类全限定名").newInstance();　

2. Student stu = Student.class.newInstance();

3. public class Student {

   private int id;

   public Student(Integer id) {
       this.id = id;
   }

   public static void main(String[] args) throws Exception {

       Constructor<Student> constructor = Student.class
               .getConstructor(Integer.class);
       Student stu3 = constructor.newInstance(123);
   }
}

3.clone接口

先实现Cloneable接口，覆写clone方法
Student stu4 = (Student) stu3.clone();

3.反序列化

// 写对象
       ObjectOutputStream output = new ObjectOutputStream(
               new FileOutputStream("student.bin"));
       output.writeObject(stu4);
       output.close();

       // 读取对象
       ObjectInputStream input = new ObjectInputStream(new FileInputStream(
               "student.bin"));
       Student stu5 = (Student) input.readObject();
       System.out.println(stu5);