策略工厂模式

父类

public abstract class Operator {

    private double d1;

    private double d2;


    public double getD1() {
        return d1;
    }

    public void setD1(double d1) {
        this.d1 = d1;
    }

    public double getD2() {
        return d2;
    }

    public void setD2(double d2) {
        this.d2 = d2;
    }
    
    public abstract double getResult();
}

加法类

public class OperatorAdd extends Operator{
    @Override
    public double getResult() {
        return this.getD1() + this.getD2();
    }
}

减法类

public class OperatorSub extends Operator{
    @Override
    public double getResult() {
        return this.getD1() - this.getD2();
    }
}

乘法类

public class OperatorMul extends Operator{
    @Override
    public double getResult() {
        return this.getD1() * this.getD2();
    }
}

除法类

public class OperatorDiv extends Operator{
    @Override
    public double getResult() {
        return this.getD1() / this.getD2();
    }
}

策略模式

public class OperatorContext {

    private Operator operator;

    public OperatorContext(String type){
        switch (type){
            case "+":
                this.operator = new OperatorAdd();
                break;
            case "-":
                this.operator = new OperatorSub();
                break;
            case "*":
                this.operator = new OperatorMul();
                break;
            case "/":
                this.operator = new OperatorDiv();
                break;
            default:
                break;
        }
    }

    public double getResult(double d1,double d2){
        this.operator.setD1(d1);
        this.operator.setD2(d2);
        return this.operator.getResult();
    }

}

使用

public static void main(String[] args) {
        OperatorContext context = new OperatorContext("+");
        double res = context.getResult(123,111);
        System.out.println(res);
    }

输出

234.0