Greenfoot: Jumping and coming back down doesn't work

Question

The player jumps but doesn't come back down, and if you hold the up arrow key, the player flies/floats, how can I fix this so the player falls back down? it would be good if source code is provided, but any help is great.

import greenfoot.*; 

public class Character extends Actor
{
double Force = 0;
double Gravity = 0.5;
double Boost_Speed = -6;
int Wait = 0;

public void act() 
{
    setLocation( getX(), (int)(getY() + Force) );
    if(Greenfoot.isKeyDown("up")){
        Wait++;
        Force = Boost_Speed;
        if(Wait >= 8)
        {   
            setLocation( getX(), (int)(getY() + 1) );
            Wait = 0;
        } 
    }
    Force = Force + Gravity;
} 

}

Answer 1

I suggest the solution by introducing the flag isJumped and getting the last key pressed with Greenfoot.getKey() method:

import greenfoot.*; 

public class Character extends Actor
{
double Force = 0;
double Gravity = 0.5;
double Boost_Speed = -6;
int Wait = 0;
private String lastKey;
private Boolean isJumped = false;
public void act() 
{
    setLocation( getX(), (int)(getY() + Force) );
    lastKey = Greenfoot.getKey();
    if(lastKey!=null && lastKey.equals("up") == true && isJumped == true) {
        isJumped = false;
    }
    if(Greenfoot.isKeyDown("up") == true && isJumped == false) {
        isJumped = true;
         Wait++;
        Force = Boost_Speed;
        if(Wait >= 8)
        {   
            setLocation( getX(), (int)(getY() + 1) );
            Wait = 0;
        } 
    }
    Force = Force + Gravity;
} 
}