1. 简单工厂模式

1.依据条件的不同，工厂类创建不同的实例。（有同一父类）

2.调用父类的方法。

3.因为不同的实例，所以会调用到子类的方法，得到不同的结果。  --->  利用多态

举例：

父类：

public abstract class Operation {
    private double numberA;
    private double numberB;

    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();

}

4个子类：

public class OperationAdd extends Operation {

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

}

public class OperationDiv extends Operation {

    @Override
    public double getResult() {
        return getNumberA() / getNumberB();
    }

}

public class OperationMul extends Operation {

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

}

public class OperationSub extends Operation {

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

}

工厂类：

public class OperationFactory {
    public static Operation creatOperation(String operate) {
        Operation operation = null;
        switch (operate) {
        case "+":
            operation = new OperationAdd();
            break;
        case "-":
            operation = new OperationSub();
            break;
        case "*":
            operation = new OperationMul();
            break;
        case "/":
            operation = new OperationDiv();
            break;
        }
        return operation;
    }

}

使用：

public class jisuanqi {
    public static void main(String[] args) {

        Operation operation = OperationFactory.creatOperation("*");
        operation.setNumberA(2);
        operation.setNumberB(1);
        System.out.println(operation.getResult());
    }

}