Java调用方法而不创建实例

问题描述

如果这个问题对普通的Java程序员来说很愚蠢，请原谅，但我对此问题感到困惑.我想从类DrawCard(Player player)中的类PoliticCard调用方法getPoliticCards().起初，我在PoliticCard中使用了static arraylist，所以我没有问题，但是我不得不更改它，因为我应该能够同时运行游戏的多个会话.

Please excuse me if this question looks dumb for a regular java programmer but i'm stuck with this problem.I want to call the method getPoliticCards() from the class PoliticCard in the class DrawCard(Player player). At first i used a static arraylist in PoliticCard so i had no problems, but i had to change it because i'm supposed to be able to run several sessions of the game at the same time.

public enum Color {
    BLACK, PURPLE
}
public class Player {
    private int id;
    private ArrayList<Color> politicCards;
    public Player(int id){
        this.setId(id);
        ArrayList<Color> array=new ArrayList<Color>();
        setPoliticCards(array);
    }
    public int getId() {
        return id;
    }
    public void setId(int id) {
        this.id = id;
    }

    public ArrayList<Color> getPoliticCards() {
        return politicCards;
    }
    public void setPoliticCards(ArrayList<Color> politicCards) {
        this.politicCards = politicCards;
    }
}
public class PoliticCard {
    private ArrayList<Color> politicCards;
    public PoliticCard(){
        setPoliticCards(new ArrayList<Color>());
        politicCards.add(Color.BLACK);
        politicCards.add(Color.PURPLE);
    }
    public ArrayList<Color> getPoliticCards() {
        return politicCards;
    }
    public void setPoliticCards(ArrayList<Color> politicCards) {
        this.politicCards = politicCards;
    }



}
public class DrawPoliticCard {
    public DrawPoliticCard(Player player){
        PoliticCard politicCard = new PoliticCard();//I know that to
//call a method from another class you should create an instance,
//but isn't *new PoliticCard();* creating a new arraylist in PoliticCard()?,
//what i want is to create the arraylist only once (like it's written in the test below)
//and then use the same updated arraylist each time i use this constructor
        player.getPoliticCards().add(politicCard.getPoliticCards().get(0));
        politicCard.getPoliticCards().remove(0);

    }

}
public class ModelPlayerTest {

    @Test
    public void testDrawCard() {
        Player player = new Player(1);
        new PoliticCard();
        new DrawPoliticCard(player);
        assertNotNull(player.getPoliticCards().get(0));
    }


}

推荐答案

从类中调用方法而不使用其真实实例的唯一方法是调用静态方法.

The only way to invoke a method from a class without using a real instance of it is by invoking a static method.

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