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里氏替换原则原则

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F嘉阳
2018-09-23 13:10:21 +08:00
parent 1433dabd23
commit 7b18f0dcf0
14 changed files with 437 additions and 8 deletions
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32
src/main/java/top/fjy8018/designpattern/principle/liskovsubstitution/classdemo/after/ARectangle.java Normal file
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package top.fjy8018.designpattern.principle.liskovsubstitution.classdemo.after;
/**
* 里氏替换原则：如果对每一个类型为S的对象o1，都有类型为T的对象o2，使得以T定义的所有程序P在所有的对象o1都代换为o2，程序P的行为没有发生变化，那么类型S是类型T的子类型
* 即：所有使用父类对象的地方替换成子类对象依然正常运行
*
* @author F嘉阳
* @date 2018-09-22 20:01
*/
public class ARectangle implements Quadrangle {
private long length;
private long width;
@Override
public long getWidth() {
return width;
}
public void setWidth(long width) {
this.width = width;
}
@Override
public long getLength() {
return length;
}
public void setLength(long length) {
this.length = length;
}
}

23
src/main/java/top/fjy8018/designpattern/principle/liskovsubstitution/classdemo/after/ASquare.java Normal file
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package top.fjy8018.designpattern.principle.liskovsubstitution.classdemo.after;
/**
* @author F嘉阳
* @date 2018-09-22 20:03
*/
public class ASquare implements Quadrangle {
private long sideLength;
@Override
public long getWidth() {
return sideLength;
}
@Override
public long getLength() {
return sideLength;
}
public void setLength(long sideLength) {
this.sideLength = sideLength;
}
}

13
src/main/java/top/fjy8018/designpattern/principle/liskovsubstitution/classdemo/after/Quadrangle.java Normal file
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package top.fjy8018.designpattern.principle.liskovsubstitution.classdemo.after;
/**
* 通过四边形接口连接，防止继承泛滥
*
* @author F嘉阳
* @date 2018-09-22 20:11
*/
public interface Quadrangle {
long getWidth();
long getLength();
}

29
src/main/java/top/fjy8018/designpattern/principle/liskovsubstitution/classdemo/before/Rectangle.java Normal file
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package top.fjy8018.designpattern.principle.liskovsubstitution.classdemo.before;
/**
* 里氏替换原则：如果对每一个类型为S的对象o1，都有类型为T的对象o2，使得以T定义的所有程序P在所有的对象o1都代换为o2，程序P的行为没有发生变化，那么类型S是类型T的子类型
* 即：所有使用父类对象的地方替换成子类对象依然正常运行
*
* @author F嘉阳
* @date 2018-09-22 20:01
*/
public class Rectangle {
private long length;
private long width;
public long getLength() {
return length;
}
public void setLength(long length) {
this.length = length;
}
public long getWidth() {
return width;
}
public void setWidth(long width) {
this.width = width;
}
}

34
src/main/java/top/fjy8018/designpattern/principle/liskovsubstitution/classdemo/before/Square.java Normal file
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package top.fjy8018.designpattern.principle.liskovsubstitution.classdemo.before;
/**
* @author F嘉阳
* @date 2018-09-22 20:03
*/
public class Square extends Rectangle {
private long sideLength;
@Override
public long getLength() {
return sideLength;
}
/**
* 覆盖了父类的实现，不满足里氏替换原则
*
* @param length
*/
@Override
public void setLength(long length) {
this.sideLength = length;
}
@Override
public long getWidth() {
return sideLength;
}
@Override
public void setWidth(long width) {
this.sideLength = width;
}
}

17
src/main/java/top/fjy8018/designpattern/principle/liskovsubstitution/method/input/after/Base.java Normal file
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package top.fjy8018.designpattern.principle.liskovsubstitution.method.input.after;
import lombok.extern.slf4j.Slf4j;
import java.util.HashMap;
/**
* @author F嘉阳
* @date 2018-09-23 11:29
*/
@Slf4j
class Base {
public void method(HashMap map) {
log.info("父类被执行");
}
}

38
src/main/java/top/fjy8018/designpattern/principle/liskovsubstitution/method/input/after/Child.java Normal file
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package top.fjy8018.designpattern.principle.liskovsubstitution.method.input.after;
import lombok.extern.slf4j.Slf4j;
import java.util.HashMap;
import java.util.Map;
/**
* 李氏转换原则要求方法入参必须比父类范围更宽，返回值必须比父类更窄
*
* @author F嘉阳
* @date 2018-09-23 11:30
*/
@Slf4j
class Child extends Base {
/**
* 方法重写，入参必须等于父类或者比父类范围更宽
* 而返回值比父类更窄已经交由IDE判断，若不符合，则编译不通过
*
* @param map
*/
@Override
public void method(HashMap map) {
log.info("子类HashMap入参方法被执行");
}
/**
* 方法重写，是子类额外的方法
*
* @param map
*/
public void method(Map map) {
log.info("子类Map入参方法被执行");
}
}

18
src/main/java/top/fjy8018/designpattern/principle/liskovsubstitution/method/input/before/Base.java Normal file
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package top.fjy8018.designpattern.principle.liskovsubstitution.method.input.before;
import lombok.extern.slf4j.Slf4j;
import java.util.Map;
/**
* @author F嘉阳
* @date 2018-09-23 11:29
*/
@Slf4j
class Base {
public void method(Map map) {
log.info("父类被执行");
}
}

18
src/main/java/top/fjy8018/designpattern/principle/liskovsubstitution/method/input/before/Child.java Normal file
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@@ -0,0 +1,18 @@
package top.fjy8018.designpattern.principle.liskovsubstitution.method.input.before;
import lombok.extern.slf4j.Slf4j;
import java.util.HashMap;
/**
* @author F嘉阳
* @date 2018-09-23 11:30
*/
@Slf4j
class Child extends Base {
public void method(HashMap map) {
log.info("子类HashMap入参方法被执行");
}
}

14
src/main/java/top/fjy8018/designpattern/principle/openclose/JavaDiscountCourse.java
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@@ -27,23 +27,25 @@ public class JavaDiscountCourse extends JavaCourse {
}
/**
* 获取原价
* 实现打折价格逻辑
*
* @return
*/
public BigDecimal getOriginPrice() {
return super.getPrice();
public BigDecimal getDistcountPrice() {
// BigDecimal推荐使用String构造器，防止精度转换问题
return super.getPrice().multiply(new BigDecimal("0.8"));
}
/**
* 实现打折价格逻辑
* 根据里氏替换原则：父类实现的方法不应该覆盖
* 获取原价
*
* @return
*/
@Override
public BigDecimal getPrice() {
// BigDecimal推荐使用String构造器，防止精度转换问题
return super.getPrice().multiply(new BigDecimal("0.8"));
return super.getPrice();
}
@Override

61
src/test/java/top/fjy8018/designpattern/principle/liskovsubstitution/classdemo/before/SquareTest.java Normal file
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package top.fjy8018.designpattern.principle.liskovsubstitution.classdemo.before;
import lombok.extern.slf4j.Slf4j;
import org.junit.jupiter.api.Test;
import top.fjy8018.designpattern.principle.liskovsubstitution.classdemo.after.ARectangle;
import top.fjy8018.designpattern.principle.liskovsubstitution.classdemo.after.Quadrangle;
@Slf4j
class SquareTest {
/**
* resize要求传入父类对象，对长宽进行设置
*
* @param rectangle
*/
public static void resize(Rectangle rectangle) {
while (rectangle.getWidth() <= rectangle.getLength()) {
rectangle.setWidth(rectangle.getWidth() + 1);
log.info("width:{} length:{}", rectangle.getWidth(), rectangle.getLength());
if (rectangle.getWidth() > 50 || rectangle.getLength() > 50) {
log.error("方法溢出");
break;
}
}
log.info("resize方法结束 width:{} length:{}", rectangle.getWidth(), rectangle.getLength());
}
public static void resize(Quadrangle quadrangle) {
while (quadrangle.getWidth() <= quadrangle.getLength()) {
// quadrangle.setWidth(quadrangle.getWidth()+1);报错，原有方法已经不能正确运行，说明原有方法设计存在问题
log.info("width:{} length:{}", quadrangle.getWidth(), quadrangle.getLength());
if (quadrangle.getWidth() > 50 || quadrangle.getLength() > 50) {
log.error("方法溢出");
break;
}
}
log.info("resize方法结束 width:{} length:{}", quadrangle.getWidth(), quadrangle.getLength());
}
@Test
void before() {
// 是长方形时业务正常运行
Rectangle rectangle = new Rectangle();
rectangle.setWidth(10);
rectangle.setLength(20);
resize(rectangle);
// 使用之类替换父类对象，业务无法运行，方法溢出
Square square = new Square();
square.setLength(40);
resize(square);
}
@Test
void after() {
// 通过里氏替换原则改造后
ARectangle aRectangle = new ARectangle();
aRectangle.setLength(20);
aRectangle.setWidth(10);
}
}

20
src/test/java/top/fjy8018/designpattern/principle/liskovsubstitution/method/input/after/ChildTest.java Normal file
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package top.fjy8018.designpattern.principle.liskovsubstitution.method.input.after;
import org.junit.jupiter.api.Test;
import java.util.HashMap;
class ChildTest {
@Test
void before() {
}
@Test
void after() {
Child child = new Child();
// 此时希望调用子类重写的方法，若子类没重写，则应执行父类的方法
child.method(new HashMap());
}
}

4
src/test/java/top/fjy8018/designpattern/principle/openclose/JavaCourseTest.java
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@@ -32,8 +32,8 @@ class JavaCourseTest {
Course course = new JavaDiscountCourse(1, "Java课程", new BigDecimal("99"));
JavaDiscountCourse javaCourse = (JavaDiscountCourse) course;
log.info("课程Id：{},课程名称：{},原价：{},折后价格：{}",
javaCourse.getId(), javaCourse.getName(), javaCourse.getOriginPrice(),
javaCourse.getPrice().setScale(2, BigDecimal.ROUND_HALF_UP));
javaCourse.getId(), javaCourse.getName(), javaCourse.getPrice(),
javaCourse.getDistcountPrice().setScale(2, BigDecimal.ROUND_HALF_UP));
}
}