Java : How to create an object in a method and use it throughout the class?

Question

public void setupPlayers() {
    System.out.println("Would you like the Code Maker to be Human or CPU? :");
    String input = mySc.next();
    if (input == "Human") {
        Player CodeMaker = new Human();
    }
    else {
        Player CodeMaker = new CPU();  
    }

public void exampleUse() {
    CodeMaker.getCode();
}

So I'm new to Java and not even sure if this is possible to begin with. The above code is all inside one class. Human is implementing the interface Player. I want to create an object CodeMaker using the class Human in the method setupPlayers, and then use this object in the method exampleUse. Is there a way to do this? If not can anyone think of any alternatives? Cheers.

why you are using an interface as a variable name? i didn't get the point — Ruelos Joel, Dec 22 '15 at 17:05
@fuzzy28 - as far as I understand, `Player` is and class impementing interface `Human`. Anyway, the sentence "an object Player using the Interface Human called CodeMaker" is a little bit confusing. — Piotr Aleksander Chmielowski, Dec 22 '15 at 17:10
^ Player is the interface, and Human is the class implementing Player. — George Burslem, Dec 22 '15 at 17:11
I thought that "Human" and "CPU" would both implement "Player" .. — Arnaud, Dec 22 '15 at 17:13
I've revised my question so hopefully it makes more sense now... — George Burslem, Dec 22 '15 at 17:23

score 3 · Accepted Answer · answered Dec 22 '15 at 17:30

I think that you must mean the Player is the interface. And remember that if you want to compare the String, you should use equals method instead of == operator.

public class ClassName{
    private Player codeMaker;

    public void setupPlayers() {
        System.out.println("Would you like the Code Maker to be Human or CPU? :");
        String input = mySc.next();
        if (input.equals("Human")) {
            codeMaker = new Human();
        }
        else {
            codeMaker = new CPU();  
        }
    }

    public void exampleUse() {
         codeMaker.getCode();
    } 
}

Thank you so much. After I added private Player codeMaker at the top it still wouldn't work, however I changed all the == for equals and it worked perfectly. — George Burslem, Dec 22 '15 at 17:34

score 2 · Answer 2 · answered Dec 22 '15 at 17:06

You may store the Player object as an instance variable :

Player CodeMaker = null;

public void setupPlayers() {
    System.out.println("Would you like the Code Maker to be Human or CPU? :");
    String input = mySc.next();
    if (input == "Human") {
        CodeMaker = new Human();
    }
    else {
        CodeMaker = new CPU();  
    }

}

public void exampleUse() {
    CodeMaker.getCode();
}

score 1 · Answer 3 · edited May 23 '17 at 11:52

Create a class field variable (private, for good encapsulation) and use "string".equals(object) to check string equality (How do I compare strings in Java?).

private Player codeMaker;

public void setupPlayers() {
    System.out.println("Would you like the Code Maker to be Human or CPU? :");
    String input = mySc.next();
    if ("Human".equals(input)) {
        codeMaker = new Human();
    }
    else {
        codeMaker = new CPU();  
    }
}

public void exampleUse() {
    codeMaker.getCode(); // you need to define a return or consumption HERE
}

Maybe you should wrap input = mySc.next() in a try/catch like this, because input read can throw an Exception.

[...]

String input = null;
try {
  input = mySc.next();
}
catch(Exception ex) {
  throw ex;
}
if ("Human".equals(input) {
    codeMaker = new Human();
}

[...]

score 0 · Answer 4 · answered Dec 22 '15 at 17:06

0

Just create a member of class: private Human CodeMaker; and initialize it in constructor CodeMaker = new Player();

Don't do Player CodeMaker = new Human(); - this should give you an error because you can't create an object of interface.

answered Dec 22 '15 at 17:06

Piotr Aleksander Chmielowski

5,640
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score 0 · Answer 5 · answered Dec 22 '15 at 17:40

0

Please, consider studying Creational Design Patterns. Java's culture is focused on organization and good architecture. You'll be certainly surprised with the world Design Patterns can give to you.

answered Dec 22 '15 at 17:40

Java : How to create an object in a method and use it throughout the class?

5 Answers5