Java类初始化和实例化

阳光穿透心脏的1/2处 2022-05-14 14:45 259阅读 0赞

Java有以下几种方式创建类对象：

*  利用new关键字
 *  利用反射Class.newInstance
 *  利用Constructor.newIntance(相比Class.newInstance多了有参和私有构造函数)
 *  利用Cloneable/Object.clone()
 *  利用反序列化

Constructor.newInstance不支持带原型入参的构造函数。

调用Class.getConstructor()方法获取无参默认构造Constructor时，**如果用户自定义了有参构造函数，因为此时java并不会生成默认构造函数**，所以Class.getConstructor()方法因找不到无参默认构造函数而抛异常。此时需要显示定义默认构造函数：

// Initialization.java
    public class Initialization {
        private int age = 2000;
        private int salary = age + 1000;
        private String name = "Tom";
    
        public Initialization() {
            print();
        }
    
        public Initialization(Integer salary, String name) {
            print();
    
            this.salary = salary;
            this.name = name;
    
            print();
        }
    
        /**
        * Static code
        */
        {
            salary += 500;
        }
    
        private void print() {
            System.out.println("age=" + this.age);
            System.out.println("salary=" + this.salary);
            System.out.println("name=" + this.name);
        }
    
        public static Initialization construct(int salary, String name) throws Exception {
            Constructor<Initialization> constructorWithNoParams = Initialization.class.getConstructor();
            Constructor<Initialization> constructorWithParams = Initialization.class.getConstructor(Integer.class, String.class);
            return salary <= 0 || name == null ? constructorWithNoParams.newInstance() : constructorWithParams.newInstance(salary, name);
        }
    
        public Initialization deSerialize() throws Exception {
            // 写对象
            ObjectOutputStream output = new ObjectOutputStream(new FileOutputStream("student.txt"));
            output.writeObject(this);
            output.close();
    
            // 读取对象
            ObjectInputStream input = new ObjectInputStream(new FileInputStream("student.txt"));
            return (Initialization) input.readObject();
        }
    }

再来看下Initialization类被编译为.class文件后的信息：

[原文链接][Link 1]

[Link 1]: http://click.aliyun.com/m/1000020096/