How to reference variables in other classes

I just feel like I'm not doing this correctly and I have researched and just can't seem to wrap my head around how to initialize variable that have to reference another method or class.

Player class

public class Player
{
   //instance variables
   private String name;
   private ScoreCard card;
   private int fullDriveYards;
   private int fullDrives;
   private int drivesOnTarget;
}

Here's the ScoreCard class variables

public class ScoreCard
{
    private int totalStrokes;
    private int versusPar;
    private LinkedList<Integer> playerScoreCard;
}

So this is how I have initialized the instance variables is Player class I did not code the Scorecard class as I didn't have to but I still added it so you can see what's going on. I just need to know if I am on the right track or completely off.

// Constructor for objects of class Player
public Player(String PlayerName)
{
       // initialize all instance variables
       // look for and handle a null reference for playerName
       // to initialize this.card create ScoreCard instance and assign reference
       this.name = PlayerName;
       PlayerName = "UNKNOWN";
       ScoreCard card = this.card;
       this.card = new ScoreCard();
       this.longestDrive = 0;
       this.fullDriveYards = 0;
       this.fullDrives = 0;
       this.drivesOnTarget = 0;
}

There are a couple things wrong with the intialization.

• didn't handle a null player name.
• Assigned an uninitialized ScoreCard to a local card variable. Didn't really hurt anything but it is redundant and that value of card will go out of scope when the constructor is finished.

Check if the player is null or has a blank name (including being empty). Note you must check if playerName is null first before attempting to check if it is blank. Otherwise, you may get a null pointer exception if the playerName is null.

For the score card, just assign the card an instance of ScoreCard. It is presumed some of your player methods will modify the scorecard as needed by simply using the field card.

// Constructor for objects of class Player
public Player(String PlayerName)
{
       // initialize all instance variables
       // look for and handle a null reference for playerName
       // to initialize this.card create ScoreCard instance and assign reference
      
       if (playerName == null || playerName.isBlank()) {
            this.name = "UNKNOWN";
       } else {
           this.name = playerName;
       }
       this.card = new ScoreCard();
       this.longestDrive = 0;
       this.fullDriveYards = 0;
       this.fullDrives = 0;
       this.drivesOnTarget = 0;
}

</details>



# 答案2
**得分**: 0

"I just feel like I'm not doing this correctly ..."
"这只是不完全正确，所以你可能得不到你想要的结果。"
In your constructor method for Player, you are assigning PlayerName to the name field, and then subsequently assigning PlayerName to "UNKNOWN".
在Player的构造方法中，你将PlayerName赋给了name字段，然后随后将PlayerName赋给了"UNKNOWN"。
Assigning PlayerName will have no effect on name.
将PlayerName分配给name将不会对name产生任何影响。
```java
this.name = PlayerName;
PlayerName = "UNKNOWN";

In your comment you mention,
在你的注释中提到，

// look for and handle a null reference for playerName

You'll need a conditional statement for this.
你需要一个条件语句来处理这个问题。

if (PlayerName == null) PlayerName = "UNKNOWN";
this.name = PlayerName;

Furthermore, you are assigning your class variable card to a new local variable card.
此外，你将类变量card分配给了一个新的局部变量card。
This, again, will have no effect, since this.card would be null at this point.
同样，这将不会产生任何效果，因为此时this.card将为null。

// to initialize this.card create ScoreCard instance and assign reference

The following will suffice.
以下内容足够了。

this.card = new ScoreCard();

So, the complete constructor should look like the following.
因此，完整的构造函数应该如下所示。

public Player(String PlayerName)
{
    // initialize all instance variables
    // look for and handle a null reference for playerName
    // to initialize this.card create ScoreCard instance and assign reference
    if (PlayerName == null) PlayerName = "UNKNOWN";
    this.name = PlayerName;
    this.card = new ScoreCard();
    this.longestDrive = 0;
    this.fullDriveYards = 0;
    this.fullDrives = 0;
    this.drivesOnTarget = 0;
}

"... I have researched and just can't seem to wrap my head around how to initialize variable that have to reference another method or class. ..."
"……我已经做了研究，但似乎无法理解如何初始化必须引用另一个方法或类的变量。"
Your assignment is correct,
你的赋值是正确的，

this.card = new ScoreCard();

Since your ScoreCard class variables are declared as private, you won't be able to access them via dot-notation—e.g., card.totalStrokes.
由于你的ScoreCard类变量声明为私有，所以你无法通过点表示法访问它们，例如card.totalStrokes。
You will need to either remove the modifier, change the modifier to public, or create methods that will provide the access.
你需要删除修饰符，将修饰符更改为public，或创建提供访问权限的方法。

public class ScoreCard
{
    private int totalStrokes;
    private int versusPar;
    private LinkedList<Integer> playerScoreCard;

    public int getTotalStrokes() {
        return totalStrokes;
    }

    public void setTotalStrokes(int totalStrokes) {
        this.totalStrokes = totalStrokes;
    }

    public int getVersusPar() {
        return versusPar;
    }

    public void setVersusPar(int versusPar) {
        this.versusPar = versusPar;
    }

    public LinkedList<Integer> getPlayerScoreCard() {
        return playerScoreCard;
    }

    public void setPlayerScoreCard(LinkedList<Integer> playerScoreCard) {
        this.playerScoreCard = playerScoreCard;
    }
}

Then, you can access the values as follows.
然后，你可以按以下方式访问这些值。

card.setTotalStrokes(123);
card.setVersusPar(123);
card.setPlayerScoreCard(new LinkedList<>());

Here are some references by Java which may help in your coding process.
以下是一些Java的参考资料，可能有助于你的编码过程。
Classes (The Java™ Tutorials > Learning the Java Language > Classes and Objects).
Lesson: Object-Oriented Programming Concepts (The Java™ Tutorials > Learning the Java Language).

this.name = PlayerName;
PlayerName = "UNKNOWN";

// look for and handle a null reference for playerName

if (PlayerName == null) PlayerName = "UNKNOWN";
this.name = PlayerName;

// to initialize this.card create ScoreCard instance and assign reference

this.card = new ScoreCard();

public Player(String PlayerName)
{
    // initialize all instance variables
    // look for and handle a null reference for playerName
    // to initialize this.card create ScoreCard instance and assign reference
    if (PlayerName == null) PlayerName = "UNKNOWN";
    this.name = PlayerName;
    this.card = new ScoreCard();
    this.longestDrive = 0;
    this.fullDriveYards = 0;
    this.fullDrives = 0;
    this.drivesOnTarget = 0;
}

this.card = new ScoreCard();

public class ScoreCard
{
    private int totalStrokes;
    private int versusPar;
    private LinkedList<Integer> playerScoreCard;

    public int getTotalStrokes() {
        return totalStrokes;
    }

    public void setTotalStrokes(int totalStrokes) {
        this.totalStrokes = totalStrokes;
    }

    public int getVersusPar() {
        return versusPar;
    }

    public void setVersusPar(int versusPar) {
        this.versusPar = versusPar;
    }

    public LinkedList<Integer> getPlayerScoreCard() {
        return playerScoreCard;
    }

    public void setPlayerScoreCard(LinkedList<Integer> playerScoreCard) {
        this.playerScoreCard = playerScoreCard;
    }
}

card.setTotalStrokes(123);
card.setVersusPar(123);
card.setPlayerScoreCard(new LinkedList<>());