场景
本例利用简单工厂模式实现加、减、乘、除计算功能：
- 定义计算操作接口（Operation），接口中定义计算方法（calculate）
- 定义加、减、乘、除计算操作实现类，实现计算接口，实现计算方法（calculate）
- 定义操作工厂类，提供创建操作类型的方法，返回 Operation
- 调用者利用工厂类获取 Operation ，进行计算处理
以上几步可以把调用者和具体实现操作隔离开来，调用者不必清楚具体计算如何实现，只需传入指令操作，获取对应操作类，调用计算方法即可完成计算功能。
UML
Code by Java
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| /**
* 计算操作接口
*
* @author jw
*/
public interface Operation {
int calculate(int firstNum, int secondNum) throws IllegalArgumentException;
}
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| /**
* 加法操作实现类
*
* @author jw
*/
public class OperationAddition implements Operation {
@Override
public int calculate(int firstNum, int secondNum) throws IllegalArgumentException {
return firstNum + secondNum;
}
}
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| /**
* 减法操作实现类
*
* @author jw
*/
public class OperationSubtraction implements Operation {
@Override
public int calculate(int firstNum, int secondNum) throws IllegalArgumentException {
return firstNum - secondNum;
}
}
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| /**
* 乘法操作实现类
*
* @author jw
*/
public class OperationMultiplication implements Operation {
@Override
public int calculate(int firstNum, int secondNum) throws IllegalArgumentException {
return firstNum * secondNum;
}
}
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| /**
* 除法操作实现类
*
* @author jw
*/
public class OperationDivision implements Operation {
@Override
public int calculate(int firstNum, int secondNum) throws IllegalArgumentException {
if(secondNum == 0){
throw new IllegalArgumentException("除数不能为0");
}
return firstNum / secondNum;
}
}
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| /**
* 计算操作工厂类
*
* @author jw
*/
public class OperationFactory {
public static Operation createOperation(String operation){
switch(operation){
case "+":
return new OperationAddition();
case "-":
return new OperationSubtraction();
case "*":
return new OperationMultiplication();
case "/":
return new OperationDivision();
default:
return null;
}
}
}
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| /**
* 应用
*
* @author jw
*/
public class TwoNumberCalculator {
private int firstNum;
private int secondNum;
private Operation operation;
public TwoNumberCalculator(){}
public TwoNumberCalculator(int firstNum, int secondNum, Operation operation){
this.firstNum = firstNum;
this.secondNum = secondNum;
this.operation = operation;
}
public int calculateResult(){
return operation.calculate(firstNum, secondNum);
}
/* getter and setter */
public static void main(String[] arg){
TwoNumberCalculator calculator = new TwoNumberCalculator(3, 4,
OperationFactory.createOperation("+"));
// The calculate result is 7
System.out.println("The calculate result is " + calculator.calculateResult());
}
}
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