工廠模式

文檔查閱說明：

Tongkey

yiibai

runoob

大話設計模式

定義：定義一個用於創建對象的接口，讓子類決定實例化哪一個類。工廠方法使一個類的實例化延遲到其子類

使用場景：

● 日誌記錄器：記錄可能記錄到本地硬盤、系統事件、遠程服務器等，用戶可以選擇記錄日誌到什麼地方；

● 數據庫訪問，當用戶不知道最後系統採用哪一類數據庫，以及數據庫可能有變化時；

● 設計一個連接服務器的框架，需要三個協議，"POP3"、"IMAP"、"HTTP"，可以把這三個作爲產品類，共同實現一個接口

 

public abstract class Operation {
	
	private double numberA = 0;
	private double numberB = 0;
	
	public double getNumberA() {
		return numberA;
	}
	public void setNumberA(double numberA) {
		this.numberA = numberA;
	}
	public double getNumberB() {
		return numberB;
	}
	public void setNumberB(double numberB) {
		this.numberB = numberB;
	}
	
	public abstract double getResult();
}

public class OperationAdd extends Operation {

	@Override
	public double getResult() {
		return this.getNumberA() + this.getNumberB();
	}

}

public class OperationSub extends Operation {

	@Override
	public double getResult() {
		return this.getNumberA() - this.getNumberB();
	}

}

public class OperationMul extends Operation {

	@Override
	public double getResult() {
		return this.getNumberA() * this.getNumberB();
	}

}

public class OperationDiv extends Operation {

	@Override
	public double getResult() {
		if(this.getNumberB() == 0) {
			try {
				throw new Exception("除數不能爲0");
			} catch (Exception e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
		}
		return this.getNumberA() / this.getNumberB();
	}

}

public class OperationFactory {

	public static Operation createOperation(String operate) {
		Operation oper = null;
		switch (operate) {
			case "+":{
				oper = new OperationAdd();
				break;
			}
			case "-":{
				oper = new OperationSub();
				break;
			}
			case "*":{
				oper = new OperationMul();
				break;
			}
			case "/":{
				oper = new OperationDiv();
				break;
			}
			default:{
				try {
					throw new Exception("操作符不匹配");
				} catch (Exception e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
		}
		
		return oper;
	}
	
	public static double getResult(String operate, double numberA, double numberB) {
		Operation oper = null;
		switch (operate) {
			case "+":{
				oper = new OperationAdd();
				break;
			}
			case "-":{
				oper = new OperationSub();
				break;
			}
			case "*":{
				oper = new OperationMul();
				break;
			}
			case "/":{
				oper = new OperationDiv();
				break;
			}
			default:{
				try {
					throw new Exception("操作符不匹配");
				} catch (Exception e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
		}
		
		oper.setNumberA(numberA);
		oper.setNumberB(numberB);
		return oper.getResult();
	}
}

public class Test {

	public static void main(String[] args) {
		Operation oper = OperationFactory.createOperation("+");
		oper.setNumberA(1);
		oper.setNumberB(2);
		double result = oper.getResult();
		System.out.println(result);
		
		System.out.println(OperationFactory.getResult("+", 1, 2));
	}

}