設計模式－原型模式

###原型模式 ####原型模式的優勢 原型模式建立對象比直接使用new建立對象性能上要好許多,爲Object類的clone方法是一個本地方法,它直接操做的是內存中的二進制流.原型模式簡化建立對象的過程,使得建立對象像粘貼複製同樣.

####使用場景 須要重複地建立類似對象時能夠考慮使用原型模式,好比在一個循環體類建立對象.

####代碼實現:

public class Prototype implements Cloneable{
    public Prototype clone(){
        Prototype prototype = null;
        try {
            prototype = (Prototype) super.clone();
        } catch (CloneNotSupportedException e) {
            e.printStackTrace();
        }
        return prototype;
    }
}

public class ConcretePrototype extends Prototype {
    public void show(){
        System.out.println("原型模式實現類:");
    }
}

public class Client {
    public static void main(String[] args) {
        ConcretePrototype cp = new ConcretePrototype();
        for (int i = 0; i < 10; i++) {
            ConcretePrototype clonecp = (ConcretePrototype) cp.clone();
            clonecp.show();
        }
    }
}

####原型模式的注意點

• 使用原型模式不會調用類的構造方法.

• 深拷貝和淺拷貝 淺拷貝: 對值類型的成員變量進行值的複製,對引用類型的成員變量只複製引用,不復制引用的對象. 深拷貝: 對值類型的成員變量進行值的複製,對引用類型的成員變量也進行引用對象的複製.

#####淺拷貝

import lombok.Data;
	@Data
	public class Student implements Cloneable{
	    private String studentName;
	    private Teacher teacher;

	    @Override
	    protected Student clone() throws CloneNotSupportedException {
	        return (Student) super.clone();
	    }

	    public Student(String studentName, Teacher teacher) {
	        this.studentName = studentName;
	        this.teacher = teacher;
	    }

	}

	@Data
	public class Teacher implements Serializable {
	    private static final long UID = 6948989635489677685L;

	    private String name;

	    public Teacher(String name) {
	        this.name = name;
	    }
	}

	public class Client {
	    public static void main(String[] args) throws Exception {
	        Teacher teacher = new Teacher("snail");
	        Student student1 = new Student("wjk",teacher);
	        Student student2 = (Student) student1.clone();
	        student2.getTeacher().setName("snail改變");
	        System.out.println(student1.getTeacher().getName());
	        System.out.println(student2.getTeacher().getName());
	     }
	}
	**運行結果**（拷貝的是引用）
	snail改變
	snail改變

#####深拷貝

@Data
	public class StudentSh implements Serializable {
	    private static final long UID = 6948989635489677685L;
	    private String studentName;
	    private Teacher teacher;

	    public StudentSh(String studentName, Teacher teacher) {
	        this.studentName = studentName;
	        this.teacher = teacher;
	    }

	    public Object deepClone() {
	        try {
	            //將對象寫到流裏
	            ByteArrayOutputStream bo = new ByteArrayOutputStream();
	            ObjectOutputStream oo = new ObjectOutputStream(bo);
	            oo.writeObject(this);
	            //從流裏讀出來
	            ByteArrayInputStream bi = new ByteArrayInputStream(bo.toByteArray());
	            ObjectInputStream oi = new ObjectInputStream(bi);
	            return (oi.readObject());
	        } catch (Exception e) {
	            return null;
	        }
	    }

	}

	public class Client {
	    public static void main(String[] args) throws Exception {
	        Teacher teacher = new Teacher("snail");

	        StudentSh student1  =new StudentSh("wjk",teacher);
	        StudentSh student2 = (StudentSh) student1.deepClone();
	        student2.getTeacher().setName("snail改變");
	        System.out.println(student1.getTeacher().getName());
	        System.out.println(student2.getTeacher().getName());
	     }
	}
	**運行結果**
	snail
	snail改變