protected void performMovement()
{
    if (Greenfoot.isKeyDown(upKey)) {
        localRotation = UP;
        if (canMove()) {
            setLocation(getX(), getY()-1);
        }
    }
    if (Greenfoot.isKeyDown(leftKey)) {
        localRotation = LEFT;
        setRotation(localRotation);
        checkTurn();
        if (canMove()) {
            move(1);
        }
    }
    if (Greenfoot.isKeyDown(downKey)) {
        localRotation = DOWN;
        if (canMove()) {
            setLocation(getX(), getY()+1);
        }
    }
    if (Greenfoot.isKeyDown(rightKey)) {
        localRotation = RIGHT;
        setRotation(localRotation);
        checkTurn();
        if (canMove()) {
            move(1);
        }
    }
}

private void checkTurn()
{
    if ((getRotation == 180) != isTurnLeft)
    {
        getImage().mirrorVertically();
        isTurnLeft = !isTurnLeft;
    }
}

isTrueLeft = true;

import greenfoot.*;
import java.util.List;

public class Player extends Actor
{   protected static final int UP = 270;
    protected static final int RIGHT = 0;
    protected static final int DOWN = 90;    
    protected static final int LEFT = 180;
    
    boolean isTrueLeft;
    
    protected String upKey = "up";
    protected String leftKey = "left";
    protected String downKey = "down";
    protected String rightKey = "right";

    protected int localRotation;
    
    public void act() 
    {
        performMovement();
    }
    
    public boolean canMove() {
        return canMove(1);
    }
    
    public boolean canMove(int distance) {
        World myWorld = getWorld();
        int x = getNextX(distance);
        int y = getNextY(distance);

        if (x >= myWorld.getWidth() || y >= myWorld.getHeight() - 1) {
            return false;
        } else if (x < 0 || y < 0) {
            return false;
        }
        List<Rock> steine = myWorld.getObjectsAt(x, y, Rock.class);
        if (steine.isEmpty()) {
            return true;
        }
        return false;
    }
    
    public int getNextX(int distance) {
        int x = getX();
        switch (localRotation) {
            case RIGHT:
                x = x + distance;
                break;
            case LEFT:
                x = x - distance;
                break;
        }
        return x;
    }
    
    public int getNextY(int distance) {
        int y = getY();
        switch (localRotation) {
            case DOWN:
                y = y + distance;
                break;
            case UP:
                y = y - distance;
                break;
        }
        return y;
    }
    
     public void move(int steps){
        if (canMove(steps)){
            super.move(steps);
        }
    }
    
    public void performMovement(){
        if (Greenfoot.isKeyDown(upKey)) {
            localRotation = UP;
            if (canMove()){
                setLocation(getX(), getY()-1);
            }
        } else if (Greenfoot.isKeyDown(leftKey)) {
            localRotation = LEFT;
            setRotation(LEFT);
            checkTurn();
            if (canMove()){
                move(1);
            }
        } else if (Greenfoot.isKeyDown(downKey)) {
            localRotation = DOWN;
            if (canMove()){
                setLocation(getX(), getY()+1);
            }
        } else if (Greenfoot.isKeyDown(rightKey)) {
            localRotation = RIGHT;
            setRotation(RIGHT);
            checkTurn();
            if (canMove()){
                move(1);
            }
        }
    }
    
    public void checkTurn() {
        if ((getRotation() == 180) != isTrueLeft)
        {
            getImage().mirrorVertically();
            isTrueLeft = !isTrueLeft;
        }
    }
}