JavaFX sample to move a character around a field based on key controls.

CharacterMovement.java

import javafx.animation.AnimationTimer;
import javafx.application.Application;
import javafx.event.EventHandler;
import javafx.scene.*;
import javafx.scene.image.*;
import javafx.scene.input.KeyEvent;
import javafx.scene.paint.Color;
import javafx.stage.Stage;

/**
 * Hold down an arrow key to have your hero move around the screen.
 * Hold down the shift key to have the hero run.
 */
public class CharacterMovement extends Application {

    private static final double W = 600, H = 400;

    private static final String HERO_IMAGE_LOC =
            "http://icons.iconarchive.com/icons/raindropmemory/legendora/64/Hero-icon.png";

    private Image heroImage;
    private Node  hero;

    boolean running, goNorth, goSouth, goEast, goWest;

    @Override
    public void start(Stage stage) throws Exception {
        heroImage = new Image(HERO_IMAGE_LOC);
        hero = new ImageView(heroImage);

        Group dungeon = new Group(hero);

        moveHeroTo(W / 2, H / 2);

        Scene scene = new Scene(dungeon, W, H, Color.FORESTGREEN);

        scene.setOnKeyPressed(new EventHandler<KeyEvent>() {
            @Override
            public void handle(KeyEvent event) {
                switch (event.getCode()) {
                    case UP:    goNorth = true; break;
                    case DOWN:  goSouth = true; break;
                    case LEFT:  goWest  = true; break;
                    case RIGHT: goEast  = true; break;
                    case SHIFT: running = true; break;
                }
            }
        });

        scene.setOnKeyReleased(new EventHandler<KeyEvent>() {
            @Override
            public void handle(KeyEvent event) {
                switch (event.getCode()) {
                    case UP:    goNorth = false; break;
                    case DOWN:  goSouth = false; break;
                    case LEFT:  goWest  = false; break;
                    case RIGHT: goEast  = false; break;
                    case SHIFT: running = false; break;
                }
            }
        });

        stage.setScene(scene);
        stage.show();

        AnimationTimer timer = new AnimationTimer() {
            @Override
            public void handle(long now) {
                int dx = 0, dy = 0;

                if (goNorth) dy -= 1;
                if (goSouth) dy += 1;
                if (goEast)  dx += 1;
                if (goWest)  dx -= 1;
                if (running) { dx *= 3; dy *= 3; }

                moveHeroBy(dx, dy);
            }
        };
        timer.start();
    }

    private void moveHeroBy(int dx, int dy) {
        if (dx == 0 && dy == 0) return;

        final double cx = hero.getBoundsInLocal().getWidth()  / 2;
        final double cy = hero.getBoundsInLocal().getHeight() / 2;

        double x = cx + hero.getLayoutX() + dx;
        double y = cy + hero.getLayoutY() + dy;

        moveHeroTo(x, y);
    }

    private void moveHeroTo(double x, double y) {
        final double cx = hero.getBoundsInLocal().getWidth()  / 2;
        final double cy = hero.getBoundsInLocal().getHeight() / 2;

        if (x - cx >= 0 &&
            x + cx <= W &&
            y - cy >= 0 &&
            y + cy <= H) {
            hero.relocate(x - cx, y - cy);
        }
    }

    public static void main(String[] args) { launch(args); }
}