接口隔离原则

介绍

客户端不要依赖不需要的接口，即一个类对另一个类的依赖应该建立在最小的接口上。

案例引入

A类，通过接口1依赖B类，C类通过依赖接口1依赖D类，A类只会用到1-3方法，C类只会使用到1，4，5方法。

uml类图

代码实现

public class Segregation1 {
    public static void main(String[] args) {
        A a = new A();
        a.dependency1(new B());
        a.dependency2(new B());
        a.dependency3(new B());

        C c = new C();
        c.dependency1(new D());
        c.dependency4(new D());
        c.dependency5(new D());
    }
}

interface Interface1{
    public void operation1();
    public void operation2();
    public void operation3();
    public void operation4();
    public void operation5();
}

class B implements Interface1{
    @Override
    public void operation1() {
        System.out.println("B 类 operation1");
    }

    @Override
    public void operation2() {
        System.out.println("B 类 operation2");
    }

    @Override
    public void operation3() {
        System.out.println("B 类 operation3");
    }

    @Override
    public void operation4() {
        System.out.println("B 类 operation4");
    }

    @Override
    public void operation5() {
        System.out.println("B 类 operation5");
    }
}

class D implements Interface1{
    @Override
    public void operation1() {
        System.out.println("D 类 operation1");
    }

    @Override
    public void operation2() {
        System.out.println("D 类 operation2");
    }

    @Override
    public void operation3() {
        System.out.println("D 类 operation3");
    }

    @Override
    public void operation4() {
        System.out.println("D 类 operation4");
    }

    @Override
    public void operation5() {
        System.out.println("D 类 operation5");
    }
}

class A{

    public void dependency1(Interface1 i){
        i.operation1();
    }
    public void dependency2(Interface1 i){
        i.operation2();
    }
    public void dependency3(Interface1 i){
        i.operation3();
    }

}

class C{
    public void dependency1(Interface1 i){
        i.operation1();
    }
    public void dependency4(Interface1 i){
        i.operation4();
    }
    public void dependency5(Interface1 i){
        i.operation5();
    }
}

案例分析

• 类A通过接口interface1依赖B，类C通过接口依赖D，因为接口interface1对于A类和C类来说，不是最小的接口，就会导致类B，类D去重写使用不到的方法
• 将接口interface1拆分成独立的接口，类A和C分别和其依赖的接口建立依赖关系。也就是采用接口隔离原则。
• 接口interface1出现的方法，也拆分成三个接口 如下图所示

案例改进

uml类图

public class Segregation2 {
    public static void main(String[] args) {
        A a = new A();
        a.dependency1(new B());
        a.dependency2(new B());
        a.dependency3(new B());

        C c = new C();
        c.dependency1(new D());
        c.dependency4(new D());
        c.dependency5(new D());
    }
}

interface Interface1 {
    public void operation1();
}

interface Interface2{
    public void operation2();
    public void operation3();
}

interface Interface3{
    public void operation4();
    public void operation5();
}


class B implements Interface1,Interface2{
    @Override
    public void operation1() {
        System.out.println("B 类 operation1");
    }

    @Override
    public void operation2() {
        System.out.println("B 类 operation2");
    }

    @Override
    public void operation3() {
        System.out.println("B 类 operation3");
    }
}

class D implements Interface1,Interface3 {
    @Override
    public void operation1() {
        System.out.println("D 类 operation1");
    }

    @Override
    public void operation4() {
        System.out.println("D 类 operation4");
    }

    @Override
    public void operation5() {
        System.out.println("D 类 operation5");
    }
}

class A{

    public void dependency1(Interface1 i){
        i.operation1();
    }
    public void dependen