题目：通过购买基金来购买股票A、B、C

public class StockA {    public void buy() {        System.out.println("股票A买入");    }    public void sell() {        System.out.println("股票A卖出");    }}public class StockB {    public void buy() {        System.out.println("股票B买入");    }    public void sell() {        System.out.println("股票B卖出");    }}public class StockC {    public void buy() {        System.out.println("股票C买入");    }    public void sell() {        System.out.println("股票C卖出");    }}

public class Fund {    StockA stockA;    StockB stockB;    StockC stockC;    public Fund() {        stockA = new StockA();        stockB = new StockB();        stockC = new StockC();    }    public void buyFund() {        stockA.buy();        stockB.buy();        stockC.buy();    }    public void sellFund() {        stockA.sell();        stockB.sell();        stockC.sell();    }}

public class Test {    public static void main(String args[]) {        Fund fund = new Fund();        fund.buyFund();        fund.sellFund();    }}

打印结果：

股票A买入股票B买入股票C买入股票A卖出股票B卖出股票C卖出

其实很简单，就是将StockA、StockB、StockC封装起来，我们只要调用Fund的API就可以了