介绍

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接口上。

Demo引入

先来看一张图：

interface MyInterface {
    void  operation1();
    void  operation2();
    void  operation3();
    void  operation4();
    void  operation5();
}
class B implements MyInterface {
    @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");
    }
}
class D implements MyInterface {
    @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");
    }
}
class A {
    //类A通过接口MyInterface依赖（使用）B类， 但是只使用1,2,3方法
    public void depand1(MyInterface myInterface) {
        myInterface.operation1();
    }
    public void depand2(MyInterface myInterface) {
        myInterface.operation2();
    }
    public void depand3(MyInterface myInterface) {
        myInterface.operation3();
    }
}
class C {
    public void depand1(MyInterface myInterface) {
        myInterface.operation1();
    }
    public void depand4(MyInterface myInterface) {
        myInterface.operation4();
    }
    public void depand5(MyInterface myInterface) {
        myInterface.operation5();
    }
}

如上图所示：类A通过接口MyInterface依赖类B，类C通过接口MyInterface依赖类D；但是，类A只是想要使用B实现的接口MyInterface中的1,2,3方法，类C想要使用类D实现的接口MyInterface中的1,4,5方法；所以，现在的设计，从接口隔离原则的角度来说，不符合“最小接口”。

改进措施：

既然接口MyInterface中的方法对于实现类来说，不是全部都需要的，那么，我们根据需求，将原来的接口进行拆分：

如图所示：将原来的一个接口拆分为三个，对应的code如下：

interface MyInterface1 {
    void operation1();
}
interface MyInterface2 {
    void operation2();
    void operation3();
}
interface MyInterface3 {
    void  operation4();
    void  operation5();
}
class B implements MyInterface1, MyInterface2 {
    @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");
    }
}
class D implements MyInterface1, MyInterface3 {
    @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");
    }
}
class A {
    //类A通过接口MyInterface依赖（使用）B类， 但是只使用1,2,3方法
    public void depand1(MyInterface1 myInterface) {
        myInterface.operation1();
    }
    public void depand2(MyInterface2 myInterface) {
        myInterface.operation2();
    }
    public void depand3(MyInterface2 myInterface) {
        myInterface.operation3();
    }
}
class C {
    public void depand1(MyInterface1 myInterface) {
        myInterface.operation1();
    }
    public void depand4(MyInterface3 myInterface) {
        myInterface.operation4();
    }
    public void depand5(MyInterface3 myInterface) {
        myInterface.operation5();
    }
}