Java 通过for循环在Arraylist中显示对象的各个元素？

我试图显示我创建的对象的各个元素

这是一个简单的Java程序，允许用户添加和跟踪播放器的详细信息

我只是被难倒了，当涉及到显示细节后，他们已经被添加。下面是我的代码

使用案例2，我可以创建对象并将其输入arraylist没有问题，但是当我尝试打印它时，我想执行以下操作

System.out.println("Player Name" + myPlayersArrayList.PlayerName + "Player Position" + myPlayerArrayList.PlayerPosition + "Player Age" + "Player Age");

我知道这是不对的，但我真的不知道该怎么办，如果有人能帮上忙，我将不胜感激。谢谢

System.out.println("Welcome to the Football Player database");
 System.out.print(System.getProperty("line.separator"));


     UserInput myFirstUserInput = new UserInput();
    int selection;
            ArrayList<Player> myPlayersArrayList = new ArrayList<Player>();

            while (true) {

                System.out.println("1. View The Players");
                System.out.println("2. Add A Player");
                System.out.println("3. Edit A Player");
                System.out.println("4. Delete A Player");
                System.out.println("5. Exit ") ;
                System.out.print(System.getProperty("line.separator"));

                selection = myFirstUserInput.getInt("Please select an option");
                System.out.print(System.getProperty("line.separator"));
                switch(selection){


        case 1: 

                        if (myPlayersArrayList.isEmpty())
                                    {
                        System.out.println("No Players Have Been Entered Yet");
                        System.out.print(System.getProperty("line.separator"));
                        break;}

                        else 
                        {for(int i = 0; i < myPlayersArrayList.size(); i++){
                            System.out.println(myPlayersArrayList);

        }
                    break;

                    case 2:  {

                        String playerName,playerPos;
                        int playerAge;

                                playerName = (myFirstUserInput.getString("Enter Player name"));
                                playerPos = (myFirstUserInput.getString("Enter Player Position"));
                                playerAge = (myFirstUserInput.getInt("Enter Player Age"));   

                                myPlayersArrayList.add(new Player(playerName, playerPos, playerAge));   ;
                                                        break;
                    }

使用案例2，我可以创建对象并将其输入arraylist没有问题，但是当我尝试打印它时，我想执行以下操作

System.out.println("Player Name" + myPlayersArrayList.PlayerName + "Player Position" + myPlayerArrayList.PlayerPosition + "Player Age" + "Player Age");

我知道这是不对的，但我真的不知道该怎么办，如果有人能帮上忙，我将不胜感激。谢谢

System.out.println("Welcome to the Football Player database");
 System.out.print(System.getProperty("line.separator"));


     UserInput myFirstUserInput = new UserInput();
    int selection;
            ArrayList<Player> myPlayersArrayList = new ArrayList<Player>();

            while (true) {

                System.out.println("1. View The Players");
                System.out.println("2. Add A Player");
                System.out.println("3. Edit A Player");
                System.out.println("4. Delete A Player");
                System.out.println("5. Exit ") ;
                System.out.print(System.getProperty("line.separator"));

                selection = myFirstUserInput.getInt("Please select an option");
                System.out.print(System.getProperty("line.separator"));
                switch(selection){


        case 1: 

                        if (myPlayersArrayList.isEmpty())
                                    {
                        System.out.println("No Players Have Been Entered Yet");
                        System.out.print(System.getProperty("line.separator"));
                        break;}

                        else 
                        {for(int i = 0; i < myPlayersArrayList.size(); i++){
                            System.out.println(myPlayersArrayList);

        }
                    break;

                    case 2:  {

                        String playerName,playerPos;
                        int playerAge;

                                playerName = (myFirstUserInput.getString("Enter Player name"));
                                playerPos = (myFirstUserInput.getString("Enter Player Position"));
                                playerAge = (myFirstUserInput.getInt("Enter Player Age"));   

                                myPlayersArrayList.add(new Player(playerName, playerPos, playerAge));   ;
                                                        break;
                    }

---

只需重写toString方法即可获得所需的输出

您需要使用索引来访问单个元素：-

for(int i = 0; i < myPlayersArrayList.size(); i++){
    System.out.println(myPlayersArrayList.get(i));
}

---

您还可以使用“for each”循环。以下是语法：

for(Class object : collectionOfObjects){
    //this will loop through the list for you and
    //now you can access each object in the list 
    //using object.property or object.method()
}

//using your example
for(Player player: myPlayersArrayList){
    System.out.println(player); //requires override of toString() method

    //or you could use
    System.out.println(player.getName());
}

---

如果只想在添加数据后立即显示数据，可以声明一个播放器引用，并使其指向添加到列表中的对象，如下所示：

Player p = new Player(playerName, playerPos, playerAge);
myPlayersArrayList.add(p);
System.out.println("Player Name" + p.PlayerName + "Player Position" + p.PlayerPosition + "Player Age" + p.playerAge);

然而，在OOP环境中，直接访问对象的属性是非常不受欢迎的，所以您应该通过get方法来检索它们。例如，要获取玩家名称，这就足够了：

public String getPlayerName(){
    return playerName;
}

如果以后要打印数据，可能应该查看迭代器模式。

列表是元素的集合。该列表提供了许多有用的方法，允许您管理它、添加、删除、设置、索引、包含，最重要的是，在本例中，还可以获取

为了操作列表中的元素，首先需要从列表中获取或检索它

列表是，这意味着您不需要使用索引for循环来访问各个成员，除非索引很重要

所以你可以

for(int i = 0; i < myPlayersArrayList.size(); i++){
    Player player = myPlayersArrayList.get(i);
    // display results
}

要显示播放器对象的内容，您可以执行许多不同的操作

您可以简单地显示播放器的各种属性，因为我无法访问您的播放器类，所以我猜测它的属性

System.out.println("Player Name: " + player.PlayerName + "; Player Position: " + player.PlayerPosition + "Player Age: " + player.PlayerAge);

或者您可以编写格式化程序方法。这可以是Player类的静态，也可以是utility类的一部分，具体取决于您的需要

System.out.println(PlayerUtils.format(player)); // Format the player properties as you see fit

或者，正如已经建议的那样，您可以覆盖播放器的toString方法

所有这些方法都有优点和缺点

我倾向于将诊断信息放入我的toString方法中，这通常对向用户显示不有用。格式化程序对于其他开发人员来说并不总是显而易见的，除非它们有很好的文档记录

您需要选择对您和您的需求最有用的内容。

您也可以在Java 8中使用forEach：

List<String> myPlayersArrayList = new ArrayList<>();
myPlayersArrayList.stream().forEach((player) -> {
    System.out.println("Player: " + player); //Override toString() in Player class
});

---

感谢您的回复，当我在末尾添加[i]时，虽然它说需要数组，但找到了ArrayList。@user1180888啊！你需要用myPlayerList.geti来获取，用myPlayerList.add来添加一些东西……哇，这真是太棒了。但它怎么知道它在使用“toString”方法呢？它看起来不像是指我。谢谢在System.out.println中放入对象名时，将自动调用toString方法。您也可以显式地调用object.toString，但正如您所看到的，这不是必需的。

System.out.println(player);

List<String> myPlayersArrayList = new ArrayList<>();
myPlayersArrayList.stream().forEach((player) -> {
    System.out.println("Player: " + player); //Override toString() in Player class
});