编写软件过程种,面临着来着耦合性,内聚性,以及可维护性,可扩展性,重用性,灵活性等多方便的挑战,设计模式是为了让程序具有一下特点
设计模式原则,其实就是程序员在编程时,应当遵守的原则,也是各种设计模式的基础(即:设计模式为什么这样设计的依据)
常用的七大原则有:
对类来说的,即一个类应该只负责一项职则。如新增和编辑功能,使用同一个类作为输入,当新增类的需求变更导致 增加或者减少字段,编辑功能可能导致执行错误。
客户端不应该依赖它不需要的接口,即一个类对另一个类的依赖应该建立在最小的接口上
观察这张图:
类A通过接口Interface1依赖B,类C通过接口Interface1依赖类D,如果接口interface1对类A和类C来说都不是最小接口,那么类B和类D都必须实现他们不需要的方法。
代码实现如下:
public interface Interface1 {
void operation1();
void operation2();
void operation3();
void operation4();
void operation5();
}
public class B implements Interface1 {
@Override
public void operation1() {
System.out.println("B实现了 operation1");
}
@Override
public void operation2() {
System.out.println("B实现了 operation2");
}
@Override
public void operation3() {
System.out.println("B实现了 operation3");
}
@Override
public void operation4() {
System.out.println("B实现了 operation4");
}
@Override
public void operation5() {
System.out.println("B实现了 operation5");
}
}
public class D implements Interface1{
@Override
public void operation1() {
System.out.println("D实现了 operation1");
}
@Override
public void operation2() {
System.out.println("D实现了 operation2");
}
@Override
public void operation3() {
System.out.println("D实现了 operation3");
}
@Override
public void operation4() {
System.out.println("D实现了 operation4");
}
@Override
public void operation5() {
System.out.println("D实现了 operation5");
}
}
public class A { //A类通过接口 Interface1 依赖B类,但是指挥用到123方法
public void depend1(Interface1 i){
i.operation1();
}
public void depend2(Interface1 i){
i.operation2();
}
public void depend3(Interface1 i){
i.operation3();
}
}
public class C {//A类通过接口 Interface1 依赖B类,但是指挥用到145方法
public void depend1(Interface1 i){
i.operation1();
}
public void depend2(Interface1 i){
i.operation4();
}
public void depend3(Interface1 i){
i.operation5();
}
}
按照隔离原则应当这样处理:
将接口interface1拆分成为独立的几个接口(我们拆成三个),类A和类C分别与他们需要的接口建立依赖关系。也就是采用接口隔离原则。
public interface Interface1 {
void operation1();
}
public interface Interface2 {
void operation2();
void operation3();
}
public interface Interface3 {
void operation4();
void operation5();
}
public class B implements Interface1,Interface2 {
@Override
public void operation1() {
System.out.println("B实现了 operation1");
}
@Override
public void operation2() {
System.out.println("B实现了 operation2");
}
@Override
public void operation3() {
System.out.println("B实现了 operation3");
}
}
public class D implements Interface1,Interface3{
@Override
public void operation1() {
System.out.println("D实现了 operation1");
}
@Override
public void operation4() {
System.out.println("D实现了 operation4");
}
@Override
public void operation5() {
System.out.println("D实现了 operation5");
}
}
public class A { //A类通过接口 Interface1 依赖B类,但是指挥用到123方法
public void depend1(Interface1 i){
i.operation1();
}
public void depend2(Interface2 i){
i.operation2();
}
public void depend3(Interface2 i){
i.operation3();
}
}
public class C {//A类通过接口 Interface1 依赖B类,但是指挥用到145方法
public void depend1(Interface1 i){
i.operation1();
}
public void depend2(Interface3 i){
i.operation4();
}
public void depend3(Interface3 i){
i.operation5();
}
}
依赖倒转原则(Dependence Inversion Principle)是指:
比如:完成一个Person类接收消息的功能
例子1:接收邮件消息
public class Email {
public String getInfo(){
return "电子邮件信息:Hello world";
}
}
public class Person {
public void receive(Email email){
System.out.println(email.getInfo());
}
}
public static void main(String[] args) {
Person person = new Person();
person.receive(new Email());
}
思考:如果我们要获取的对象是 微信,短信等等,则新增类,同时Person也要增加对应的方法
解决思路:引入一个抽象的接口IReceiver,表示接收者,这样Person类与接口IReceiver发生依赖,因为Email,WerXin等等属于接收范围,他们各自实现IReceiver接口就OK了,这样就符合依赖倒置原则。
代码如下:
/**
* @Author:lpj
* @name:IReceiver
* @Date:2023/12/13 14:59
* @describe:定义接口
*/
public interface IReceiver {
public String getInfo();
}
public class Email implements IReceiver{
@Override
public String getInfo() {
return "电子邮件信息:Hello world";
}
}
public class WeiXin implements IReceiver{
@Override
public String getInfo() {
return "微信消息:hello,ok";
}
}
public class Person {
public void receive(IReceiver receiver){
System.out.println(receiver.getInfo());
}
}
public static void main(String[] args) {
Person person = new Person();
person.receive(new Email());
person.receive(new WeiXin());
}
public interface IReceiver {
public String getInfo();
}
public class Email implements IReceiver {
@Override
public String getInfo() {
return "电子邮件信息:Hello world";
}
}
public class WeiXin implements IReceiver{
@Override
public String getInfo() {
return "微信消息:hello,ok";
}
}
public class Person {
private IReceiver receiver;//成员
public Person(IReceiver receiver){
this.receiver = receiver;
}
public void getMessage(){
System.out.println(receiver.getInfo());
}
}
public static void main(String[] args) {
Person person = new Person(new WeiXin());
Person person1 = new Person(new Email());
person.getMessage();
person1.getMessage();
}
setter方式传递代码实现如下(主要代码也是在Person类)
public class Person {
private IReceiver receiver;//成员
// public Person(IReceiver receiver){
// this.receiver = receiver;
// }
public void setReceiver(IReceiver receiver) {
this.receiver = receiver;
}
public void getMessage(){
System.out.println(receiver.getInfo());
}
}
public static void main(String[] args) {
Person person = new Person();
Person person1 = new Person();
person.setReceiver(new WeiXin());
person1.setReceiver(new Email());
person.getMessage();
person1.getMessage();
}
public class A {
public int func1(int num1,int num2){
return num1-num2;
}
}
public class B extends A {
//这里重写了A类的方法,可能是无意识
public int func1(int a,int b){
return a+b;
}
public int func2(int a,int b){
return func1(a,b) +9;
}
}
public static void main(String[] args) {
A a = new A();
System.out.println("11-3=" + a.func1(11,3));
System.out.println("1-8=" + a.func1(1,8));
System.out.println("-----------------------------");
B b = new B();
System.out.println("11-3=" + b.func1(11,3));
System.out.println("1-8=" +b.func1(1,8));
System.out.println("11+3+9=" +b.func2(11,3));
}
代码实现:
public class Base {
//更加基础的方法和成员写道该类
public int Base;
public void BaseMethod(){
}
}
public class A extends Base{
public int func1(int num1,int num2){
return num1-num2;
}
}
public class B extends Base {
//B使用A类的方法,使用组合关系
private A a = new A();
//这里重写了A类的方法,可能是无意识
public int func1(int a,int b){
return super.Base+a+b;
}
public int func2(int a,int b){
return func1(a,b) +9;
}
public int func3(int a,int b){
return this.a.func1(a,b);
}
@Override
public void BaseMethod() {
super.BaseMethod();
}
}
public class Shape { //基类
public int m_type;
}
public class Rectangle extends Shape {
Rectangle(){
super.m_type =1;
}
}
public class Circle extends Shape {
Circle(){
super.m_type = 2;
}
}
public class Triangle extends Shape{ //新增一个图形
Triangle(){
super.m_type = 3;
}
}
public class GraphicEditor {
public void drawShape(Shape s){
if (s.m_type==1)
drawRectangle(s);
else if (s.m_type ==2)
drawCircle(s);
else if (s.m_type==3)
drawTriangle(s);
}
public void drawRectangle(Shape r){
System.out.println("绘制矩形");
}
public void drawCircle(Shape r){
System.out.println("绘制圆形");
}
public void drawTriangle(Shape r){
System.out.println("绘制三角形");
}
}
//调用
public static void main(String[] args) {
GraphicEditor graphicEditor = new GraphicEditor();
graphicEditor.drawShape(new Circle());
graphicEditor.drawShape(new Rectangle());
graphicEditor.drawShape(new Triangle());
}
分析一下:
思路:把创建Shape 类做成一个抽象类,并提供一个抽象的draw方法,让子类去实现即可,这样我们有新的图形种类时,只需要让新的图形类继承shape,并实现draw方法,使用方的代码就不用修改,满足了开闭原则。
代码如下:
public abstract class Shape { //基类
public int m_type;
public abstract void draw();
}
public class Triangle extends Shape{ //新增一个图形
Triangle(){
super.m_type = 3;
}
@Override
public void draw() {
System.out.println("绘制三角形");
}
}
public class Rectangle extends Shape {
Rectangle(){
super.m_type =1;
}
@Override
public void draw() {
System.out.println("绘制矩形");
}
}
public class Circle extends Shape {
Circle(){
super.m_type = 2;
}
@Override
public void draw() {
System.out.println("绘制圆形");
}
}
public class GraphicEditor {
public void drawShape(Shape s){
s.draw();
}
}
//调用
public static void main(String[] args) {
GraphicEditor graphicEditor = new GraphicEditor();
graphicEditor.drawShape(new Circle());
graphicEditor.drawShape(new Rectangle());
graphicEditor.drawShape(new Triangle());
}
1.有一个学校,下属有各个学院和总部,现要求打印出学校总部员工ID和学院员工ID
代码实现如下:
public class CollegeEmployee { //学院员工类
private String id;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
}
public class Employee { //总部员工类
private String id;
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
}
public class CollegeManager { //管理学院员工的管理类
public List<CollegeEmployee> getAllEmployee(){
List<CollegeEmployee> list = new ArrayList<>();
for (int i = 0; i < 10; i++) {
CollegeEmployee employee = new CollegeEmployee();
employee.setId("学院员工id:"+i);
list.add(employee);
}
return list;
}
}
public class SchoolManager {
public List<Employee> getAllEmployee(){
List<Employee> list = new ArrayList<>();
for (int i = 0; i < 5; i++) {
Employee employee = new Employee();
employee.setId("学校总部员工id:" +i);
list.add(employee);
}
return list;
}
//该方法完成输出学院总部和学院员工信息id
void printAllEmployee(CollegeManager sub){
//学院员工
List<CollegeEmployee> list1 = sub.getAllEmployee();
for (CollegeEmployee e :list1){
System.out.println(e.getId());
}
//学校总部员工
List<Employee> list2 = this.getAllEmployee();
for (Employee e :list2){
System.out.println(e.getId());
}
}
}
//调用
public static void main(String[] args) {
SchoolManager schoolManager = new SchoolManager();
schoolManager.printAllEmployee(new CollegeManager());
}
主要把SchoolManager 类中 CollegeManager 的具体实现剥离开,在它自己类中实现,在SchoolManager中调用方法即可。
public class CollegeManager { //管理学院员工的管理类
public List<CollegeEmployee> getAllEmployee(){
List<CollegeEmployee> list = new ArrayList<>();
for (int i = 0; i < 10; i++) {
CollegeEmployee employee = new CollegeEmployee();
employee.setId("学院员工id:"+i);
list.add(employee);
}
return list;
}
//输出学院员工的信息
public void printEmployee(){
List<CollegeEmployee> allEmployee = getAllEmployee();
for(CollegeEmployee e:allEmployee){
System.out.println(e.getId());
}
}
}
public class SchoolManager {
public List<Employee> getAllEmployee(){
List<Employee> list = new ArrayList<>();
for (int i = 0; i < 5; i++) {
Employee employee = new Employee();
employee.setId("学校总部员工id:" +i);
list.add(employee);
}
return list;
}
//该方法完成输出学院总部和学院员工信息id
void printAllEmployee(CollegeManager sub){
//学院员工
sub.printEmployee();
//学校总部员工
List<Employee> list2 = this.getAllEmployee();
for (Employee e :list2){
System.out.println(e.getId());
}
}
}
原则时尽量使用合成/聚合的方式,而不是继承