1. 基础
工厂模式，让创建实例的过程封装到工厂类中，避免耦合
工厂类中创建对象的方法一般都是 create 开头，但有的也命名为 getInstance()、createInstance()、newInstance()，有的甚至命名为 valueOf()（比如 Java String 类的 valueOf() 函数）等等
1.1 简单工厂
简单工厂模式（Simple Factory Pattern）又叫作静态工厂方法模式（Static Factory Method Pattern）
简单工厂模式的最大优点在于工厂类中包含必要的逻辑判断，根据客户端的选择条件动态实例化相关的类，对于客户端来说，去除了与具体产品的依赖
增加操作：
不但对扩展开放了，对修改也开放了违背的是开放-封闭原则
1.2 工厂方法
工厂方法模式(Factory Method)，定义一个用于创建对象的接口，让子类决定实例化哪一个类。工厂方法使一个类的实例化延迟到其子类
2. 实战：四则运算
public static double calculate(String operator, double num1, double num2) {
double result = 0;
switch (operator) {
case "+":
result = num1 + num2;
break;
case "-":
result = num1 - num2;
break;
case "*":
result = num1 * num2;
break;
case "/":
if (num2 == 0) {
throw new ArithmeticException("num2 is zero");
}
result = num1 / num2;
break;
}
return result;
}
3 优化一：简单工厂模式
image.png
@Test
public void test() {
Operation operation = OperationFactory.createOperation("+");
double result = operation.calculate(10, 1);
System.out.println(result);
}
3.1 运算工厂类 OperationFactory
简单运算工厂类 OperationFactory 负责实例化具体的运算对象
public class OperationFactory {
public static Operation createOperation(String operator) {
Operation operation = null;
switch (operator) {
case "+":
operation = new Addition();
break;
case "-":
operation = new Subtract();
break;
case "*":
operation = new Multiply();
break;
case "/":
operation = new Division();
break;
}
return operation;
}
}
3.2 抽象运算类和它的子类
public abstract class Operation {
public abstract double calculate(double num1, double num2);
}
public class Addition extends Operation {
@Override
public double calculate(double num1, double num2) {
return num1 + num2;
}
}
public class Subtract extends Operation {
@Override
public double calculate(double num1, double num2) {
return num1 - num2;
}
}
public class Multiply extends Operation {
@Override
public double calculate(double num1, double num2) {
return num1 * num2;
}
}
public class Division extends Operation {
@Override
public double calculate(double num1, double num2) {
if (num2 == 0) {
throw new ArithmeticException("num2 is zero");
}
return num1 / num2;
}
}
4. 优化二：工厂方法模式
image.png
@Test
public void test() {
Operation operation = OperationFactory.createOperation("pow");
double result = operation.calculate(2, 4);
System.out.println(result);
}
4.1 运算工厂类
public class OperationFactory {
public static Operation createOperation(String operator) {
Operation operation = null;
IFactory factory = null;
switch (operator) {
case "+":
case "-":
case "*":
case "/":
factory = new BasicFactory();
break;
case "pow":
case "log":
factory = new AdvancedFactory();
break;
}
// 多态
operation = factory.createOperation(operator);
return operation;
}
}
分析：
新的 OperationFactory 类已经不存在运算子类实例化的代码。也就是说，在这个代码里，全部是接口与具体工厂类，并不存在具体的实现，与原来的OperationFactory 类对比，实例化的过程延迟到了工厂子类中
4.2 工厂接口 IFactory
public interface IFactory {
Operation createOperation(String operator);
}
基础运算工厂和高级运算工厂
public class BasicFactory implements IFactory {
@Override
public Operation createOperation(String operator) {
Operation operation = null;
switch (operator) {
case "+":
operation = new Addition();
break;
case "-":
operation = new Subtract();
break;
case "*":
operation = new Multiply();
break;
case "/":
operation = new Division();
break;
}
return operation;
}
}
public class AdvancedFactory implements IFactory {
@Override
public Operation createOperation(String operator) {
Operation operation = null;
switch (operator) {
case "pow":
operation = new Pow();
break;
case "log":
operation = new Log();
break;
}
return operation;
}
}
public class Pow extends Operation {
@Override
public double calculate(double num1, double num2) {
return Math.pow(num1, num2);
}
}
public class Log extends Operation {
/**
* 取对数：以 num1 为底的 num2 的对数
*/
@Override
public double calculate(double num1, double num2) {
return Math.log(num2) / Math.log(num1);
}
}
