《大话设计模式》--策略模式

题目：商场做活动，有三种：正常收费、满300返100、打8折

效果图：

下面是策略和工厂结合

public abstract class Strategy {
    public abstract double acceptCash(double money);
}

public class StrategyNormal extends Strategy {
    @Override
    public double acceptCash(double money) {
        return money;
    }
}

public class StrategyReturn extends Strategy {

    private double moneyCondition;
    private double moneyReturn;

    public StrategyReturn(String moneyCondition, String moneyReturn) {
        this.moneyCondition = Double.parseDouble(moneyCondition);
        this.moneyReturn = Double.parseDouble(moneyReturn);
    }

    @Override
    public double acceptCash(double money) {
        double result = 0;
        if (money >= moneyCondition) {
            result = money - Math.floor(money / moneyCondition) * moneyReturn;
        }
        return result;
    }
}

public class StrategySale extends Strategy {
    private double sale;

    public StrategySale(String sale) {
        this.sale = Double.parseDouble(sale);
    }

    @Override
    public double acceptCash(double money) {
        return money * sale;
    }
}

public class ContextStrategy {
    private Strategy strategy;

    public ContextStrategy(String type) {
        switch (type) {
            case "正常收费":
                strategy = new StrategyNormal();
                break;
            case "满300返100":
                strategy = new StrategyReturn("300", "100");
                break;
            case "打8折":
                strategy = new StrategySale("0.8");
                break;
        }
    }

    public double contextImpl(double money) {
        double result = 0;
        if (null != strategy) {
            result = strategy.acceptCash(money);
        }
        return result;
    }
}

public class StrategyActivity extends AppCompatActivity {
    private Spinner spinner;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_strategy);
        spinner = (Spinner) findViewById(R.id.spinner);
        spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
            @Override
            public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
                TextView textView = (TextView) view;
                ContextStrategy contextStrategy = new ContextStrategy(textView.getText().toString());
                Toast.makeText(StrategyActivity.this, contextStrategy.contextImpl(1000) + "", Toast.LENGTH_SHORT).show();
            }

            @Override
            public void onNothingSelected(AdapterView<?> parent) {

            }
        });
    }
}

布局

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.administrator.schema1.StrategyFactory.StrategyActivity">

    <Spinner
        android:id="@+id/spinner"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:entries="@array/spinner"></Spinner>
</RelativeLayout>

arrays.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string-array name="spinner">
        <item>正常收费</item>
        <item>满300返100</item>
        <item>打8折</item>
    </string-array>
</resources>

 ContextStrategy是策略类，它创建对象且调用策略，判断条件不要写在StartegyActivity（客户端）

简单工厂模式和策略模式的区别：

简单工厂模式通过多态能得到抽象父类，它注重的是对象；而策略模式不关心对象，策略类封装了方法，直接调用就可以了。