CODEWITHSUNDEEP
javaarraylist
Mistweaver
Mistweaver

Reputation: 25

ArrayList cannot resolve variable type

Attempting to get a custom class known as DrawGraphics to contain an ArrayList of custom objects instead of a single Sprite. However the ArrayList refuses to accept the new Bouncer object, and when it does, the rest of the DrawGraphics class does not recognize it.

Original Code

package objectssequel;

import java.util.ArrayList;
import java.awt.Color;
import java.awt.Graphics;

public class DrawGraphics {
    Bouncer movingSprite;  //this was the original single sprite

    /** Initializes this class for drawing. */
    public DrawGraphics() {
        Rectangle box = new Rectangle(15, 20, Color.RED);
        movingSprite = new Bouncer(100, 170, box);
        movingSprite.setMovementVector(3, 1);
    }

    /** Draw the contents of the window on surface. */
    public void draw(Graphics surface) {
    movingSprite.draw(surface);
    }
}

Attempted Solution: First I created the ArrayList of objects of class Bouncer

ArrayList<Bouncer> bouncerList = new ArrayList<Bouncer>();

All good. I first then inserted the following code on the line below this

bouncerList.add(movingSprite);

This generated a "Syntax error on token(s), misplaced construct(s)" and "Syntax error on token "movingSprite", VariableDeclaratorId expected after this token" compiler error. I guessed this might be because I used the bouncerList.add() outside of a method body, so I created the following method for the class DrawGraphics

    public void addBouncer(Bouncer newBouncer) {
        bouncerList.add(newBouncer);
    }

I then called this method in DrawGraphics() with:

addBouncer(movingSprite);

the compiler error informed me that movingSprite could not be resolved to a variable type. I attempted this:

 public void addBouncer() {
        Bouncer movingSprite;
        bouncerList.add(movingSprite);
    }

Then attempted to initialize movingSprite by giving it a null setting, and no such luck as well, and probably a dozen other combinations ways to fix this. Any solutions? How do I create an ArrayList of Bouncer objects within the DrawGraphics Class?

Edit: Is it possible to not use and remove 'Bouncer movingSprite' from the original code and create an instance of the object just from the bouncerList.add()?

Upvotes: 0

Views: 603

Answers (2)

Judge Mental
Judge Mental

Reputation: 5239

You are trying to declare and initialize the array at object construction time? Sadly, java collections makes this seemingly obvious use case awkward.

List< Bouncer > bouncerList = new ArrayList< Bouncer >() { {
    add( new Bouncer() );
} };

This may lead to difficulty serializing your DrawGraphics class if ever that becomes necessary. Why not populate it in the DrawGraphics constructor?

Another option:

List< Bouncer > bouncerList = new ArrayList< Bouncer >( Arrays.asList( new Bouncer() ) );

You can also use guava's Lists utility class to construct and populate an array list in a single line.

Upvotes: 0

Scary Wombat
Scary Wombat

Reputation: 44834

In this code

public void addBouncer(Bouncer newBouncer) {
        bouncerList.add(Bouncer);               // this is trying to add a class
    }

you need to change to

public void addBouncer(Bouncer newBouncer) {
    bouncerList.add(newBouncer);             // this will add the object
}

and after

  movingSprite.setMovementVector(3, 1);

call

  addBouncer (movingSprite);

Upvotes: 1

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