Sample code for implementing simple factory pattern in Java (picture)

Factory pattern is a creational pattern

Simple factory pattern

Class diagram

Use a factory class to create the corresponding object based on a condition

//业务功能
public interface ICalculation {
	double getResult(double numA, double numB);
}

public class CalcAdd implements ICalculation {

	@Override
	public double getResult(double numA, double numB) {
		System.out.println("加法");
		return numA + numB;
	}

}

public class CalcSubtract implements ICalculation {

	@Override
	public double getResult(double numA, double numB) {
		System.out.println("减法");
		return numA - numB;
	}

}

/*
 * 简单工厂模式 关注：对象的创建
 * 建立一个工厂类，对实现了同一接口的或者是存在继承关系的一些类进行实例的创建
 */
public class Test4Simple {
	public static void main(String[] args) {
//		String operation = "/";
		String operation = "+";
//		String operation = "-";
//		String operation = "*";
		double numA = 182, numB = 33;
		ICalculation createCalc = CalcSimpleFactory.createCalc(operation);
		double result = createCalc.getResult(numA, numB);
		System.out.println(result);
	}
}

Defects of a simple factory: When a simple factory creates a product, it needs to pass the corresponding parameters. If the transmission is incorrect, the object cannot be obtained.

Improvement: multiple methods to create different products

Class diagram

public class CalcMultipleFactory {
	
	public static ICalculation produceAdd() {
		return new CalcAdd();
	}
	
	public static ICalculation produceSubtract() {
		return new CalcSubtract();
	}
	
	public static ICalculation produceMultiply() {
		return new CalcMultiply();
	}
	
	public static ICalculation producepide() {
		return new Calcpide();
	}
}

public class Test4Multiple {

	public static void main(String[] args) {
		double numA = 182, numB = 33;
		
		ICalculation createCalc = CalcMultipleFactory.produceAdd();
		double result = createCalc.getResult(numA, numB);
		System.out.println(result);
		
		createCalc = CalcMultipleFactory.produceSubtract();
		result = createCalc.getResult(numA, numB);
		System.out.println(result);
		
		createCalc = CalcMultipleFactory.produceMultiply();
		result = createCalc.getResult(numA, numB);
		System.out.println(result);
		
		createCalc = CalcMultipleFactory.producepide();
		result = createCalc.getResult(numA, numB);
		System.out.println(result);
	}
}

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