java开闭原则实例
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2022-03-15 15:36:44
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题记:
以后想多写几篇blog,不为别的,为了加深自己学习印象吧。也许有人会问,你都做java这么久了还在学这些啊,没错,正是因为我做久了java,才发现自己的基础知识有些欠缺,概念懂一些,但未必深刻,所以还要再学一下下。。。
java开闭原则,即对扩展开放,对修改关闭。这样原则设计出来的系统,遇到增加功能的需求时,几乎不用修改源代码,只是增加几个类,然后调用就好。这样既增加了新功能满足了需求,又维护了原本系统的稳定性。
下面我会写一个demo,具体分为5步,作用是比较两个事物的大小,比如可以比较2个人的大小、2个房子的大小、2头猪的大小等,看了demo瞬间明白。
一、类图
二、需要比较的对象,暂时只有房子、人
//房子
public class House {
int width;
int length;
String addr;
public House (int width, int length, String addr){
this.width = width;
this.length = length;
this.addr = addr;
}
public int getWidth() {
return width;
}
public void setWidth(int width) {
this.width = width;
}
public int getLength() {
return length;
}
public void setLength(int length) {
this.length = length;
}
public String getAddr() {
return addr;
}
public void setAddr(String addr) {
this.addr = addr;
}
public int getSquare() {
return width * length;
}
@Override
public String toString() {
return "House [width=" + width + ", length=" + length + ", addr="
+ addr + "]";
}
}
//人
public class Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Person [name=" + name + ", age=" + age + "]";
}
}
三、抽象类,把随着比较对象不同而改变的方法抽象出来
public abstract class CompareObject {
protected Object object1;
protected Object object2;
public void setData(Object arg1, Object arg2){
if (isAccept(arg1,arg2)) {
object1 = arg1;
object2 = arg2;
}else {
throw new RuntimeException( arg1 + " and " + arg2 + " isn't the them type ");
}
}
protected abstract boolean isAccept(Object arg1, Object arg2);
public abstract Object getMax();
public abstract Object getMin();
}
/**
* @author lei
*
*/
public class ComparePerson extends CompareObject{
@Override
public Object getMax() {
Person person1 = (Person) object1;
Person person2 = (Person) object2;
if (person1.getAge() > person2.getAge()) {
return person1;
}
return person2;
}
@Override
public Object getMin() {
if (((Person) object1).getAge() > ((Person) object2).getAge()) {
return (Person) object2;
}
return (Person) object1;
}
@Override
protected boolean isAccept(Object arg1, Object arg2) {
if ((arg1 instanceof Person) && (arg2 instanceof Person)) {
return true;
}
return false;
}
}
public class CompareHouse extends CompareObject {
@Override
protected boolean isAccept(Object arg1, Object arg2) {
if ((arg1 instanceof House) && (arg2 instanceof House)) {
return true;
}
return false;
}
@Override
public Object getMax() {
if (((House) object1).getSquare() > ((House) object2).getSquare()) {
return (House) object1;
}
return (House) object2;
}
@Override
public Object getMin() {
if (((House) object1).getSquare() > ((House) object2).getSquare()) {
return (House) object2;
}
return (House) object1;
}
public Object getCheaper() {
return null;
}
}
五、最后的调用
public class MainClass {
public static void main(String[] args) {
Person person1 = new Person("petter", 20);
Person person2 = new Person("mery", 21);
ComparePerson comparePerson = new ComparePerson();
comparePerson.setData(person1, person2);
System.out.println("max_person: " + comparePerson.getMax().toString());
//house
House house1 = new House(8,12," ShangHai ");
House house2 = new House(10,11," ShenZheng ");
CompareHouse compareHouse = new CompareHouse();
compareHouse.setData(house1, house2);
System.out.println("max_House: " + compareHouse.getMax().toString());
}
}
打印结果:
max_person: Person [name=mery, age=21]
max_House: House [width=10, length=11, addr= ShenZheng ]
好了,demo已经结束,差不多已经明白了吧。这样做的好处就是,如果下次要添加比较2头猪的需求时,我们无需改动原本的代码,只要添加一个pig类、一个ComparePig类就好了。