Java 对象的创建方式

• 1、new关键字
• 2、Class.newInstance()
• 3、Constructor.newInstance()
• 4、Clone()方法
• 5、反序列化

Employee 对象构建

package com.coffee;

public class Employee implements Cloneable, Serializable {

    private static final long serialVersionUID = 1L;

    private String name;

    public Employee() {
        System.out.println("Employee Constructor Called...");
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        Employee other = (Employee) obj;
        if (name == null) {
            if (other.name != null) {
                return false;
            }
        } else if (!name.equals(other.name)) {
            return false;
        }
        return true;
    }

    @Override
    public String toString() {
        return "Employee [name=" + name + "]";
    }

    @Override
    public Object clone() {
        Employee employee = null;
        try {
            employee = (Employee) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return employee;
    }
}

Employee emp1 = new Employee();
emp1.setName("Naresh");

• 会调用构造方法

Employee emp2 = (Employee) Class.forName("com.coffee.Employee").newInstance();
// Or we can simply do this
// Employee emp = Employee.class.newInstance();
emp2.setName("Rishi"); 

• 会调用构造方法

# 无参构造器必须是 public，否则会抛出 java.lang.NoSuchMethodException: com.coffee.Employee.()
Constructor constructor = Employee.class.getConstructor();
Employee emp3 = constructor.newInstance();
emp3.setName("Yogesh");

# 无参构造器是非 public 时的解决方案：
Constructor declaredConstructor = Employee.class.getDeclaredConstructors()[0];
declaredConstructor.setAccessible(true);
Employee emp3 = (Employee) declaredConstructor.newInstance();
emp3.setName("Yogesh");

• 会调用构造方法

Employee emp4 = (Employee) emp3.clone();
emp4.setName("Atul");

• 不会调用构造方法
• 对象必须实现 Cloneable 接口并复写 Object 的 clone() 方法
• clone() 方法默认是浅拷贝的，即返回一个新的对象，但是新对象里的引用类型变量地址指向的还是原对象内引用类型的地址（对象不同，内部引用相同，拷贝地址）

深拷贝：创建一个新的对象和数组，将原对象各项属性的“值”拷贝过来（拷贝值）

// Serialization
ObjectOutputStream out = new ObjectOutputStream(new FileOutputStream("data.obj"));
out.writeObject(emp4);
out.close();

//Deserialization
ObjectInputStream in = new ObjectInputStream(new FileInputStream("data.obj"));
Employee emp5 = (Employee) in.readObject();
in.close();
emp5.setName("Akash");

• 不会调用构造方法
• 类必须实现Serializable接口