FROG JUMP

setLocation(getX()-10, getY()); // move left

if (isTouching(Wall.class)) {
    setLocation(getX()+10, getY()); // undo move to the left
}

import greenfoot.*;  // (World, Actor, GreenfootImage, Greenfoot and MouseInfo)

/**
 * Write a description of class Frog here.
 * 
 * @author (your name) 
 * @version (a version number or a date)
 */
public class Frog extends Actor {    
    /**
     * Act - do whatever the Frog wants to do. This method is called whenever
     * the 'Act' or 'Run' button gets pressed in the environment.
     */
    
    private int vSpeed = 0;
    private int acceleration = 1;
    private int jumpHeight = -20;
    
    private GreenfootImage images = getImage();
    private String[] imageNames = {"frog0.png", "frog1.png", "frog2.png", "frog3.png", "frog4.png", "frog5.png", "frog6.png", "frog7.png"};
    private int currentImage = 0;
    int xPos;
    int yPos;
    
    public Frog() {
    }
    
    public void addedToWorld(World world) {
        xPos = getX();
        yPos = getY();
    }
    
    public void act() {        
        if (Greenfoot.isKeyDown("left")) {
            setLocation(getX()-10, getY());
            if (isTouching(Block32.class)) {
                setLocation(getX()+10, getY());
            }
        }
        if (Greenfoot.isKeyDown("right")) {
            setLocation(getX()+10, getY());
            if (isTouching(Block32.class)) {
                setLocation(getX()-10, getY());
            }
        }
        if (Greenfoot.isKeyDown("up") && (onBlock32() == true)) {
            vSpeed = jumpHeight;
            fall();
        }
        
        checkFalling();
        animate();
    }
    
    public void fall() {
        setLocation(getX(), getY() + vSpeed);
        vSpeed = vSpeed + acceleration;
    }
    
    private boolean onBlock32() {
        Actor under = getOneObjectAtOffset(0, getImage().getHeight()/2, Block32.class);
        return under != null;
    }

    public void checkFalling() {
        if ((onBlock32() == false)) {
            fall();
        }
        if ((onBlock32() == true)) {
            vSpeed = 0;
        }
    }
    
    private void animate() {
        if (getX() != xPos || getY() != yPos) {
            currentImage++;
            if (currentImage >= imageNames.length) 
                currentImage = 0;
                
                GreenfootImage newImage = new GreenfootImage(imageNames[currentImage]);
                
                if (getX() < xPos) 
                    newImage.mirrorHorizontally();
                                
                setImage(newImage);
                images = getImage();
            
        }
        xPos = getX();
        yPos = getY();
    }
}

    private boolean onBlock32() {
        Actor under = getOneObjectAtOffset(0, getImage().getHeight() / 2 + 1, Block32.class);
        return under != null;
    }

    public void checkFalling() {
        if ((onBlock32() == false)) {
            fall();
        }
        if ((onBlock32() == true)) {
            vSpeed = 0;
            placeOnBlock();
        }
    }    

    private void placeOnBlock() {
        final Actor belowBlock = this.getOneObjectAtOffset(0, getImage().getHeight() / 2, Block32.class);
        if (belowBlock != null) {
            setLocation(getX(), belowBlock.getY() - belowBlock.getImage().getHeight() / 2 - getImage().getHeight() / 2 - 1);
        }
    }

public class TempWorld extends World
{
    private World world;
    
    public TempWorld(World w)
    {
        super(600, 400, 1);
        world = w; // save scrolling world
        prepare();
    }
    
    ...
    
    public void act()
    {
        if (...) Greenfoot.setWorld(world); // return to scrolling world
    }
}

// in World subclass
if (...) Greenfoot.setWorld(new TempWorld(this));

// or, in Actor subclass
if (...) Greenfoot.setWorld(new TempWorld(getWorld()));