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();
}
}
总结
接口的设计尽量要小
这是接口隔离的核心,当然过小的接口会导致项目结构的负责度增加,在实际使用中,要合理把握尺度。
接口要高内聚
即接口尽量少的公布public方法,在项目开发中,接口通常充当规范来使用,是一种承诺,承诺越少越有利于系统开发。