Moon lander, gravity + velocity for an image

Question

Hey its my first year doing java so I'm still quite bad.

I'm making a lunar lander for my coursework and I'm struggling to make some kind of gravity to pull my rocket with increasing speed, and I cant find a way of my rocket to move with increasing speed in any direction. Here is my code

import javax.swing.JFrame;

import java.awt.Color;          


import java.util.Random;
import javax.swing.Timer;

import java.awt.event.*;        

import java.awt.;

import javax.swing.;

import java.awt.image.BufferedImage; 

public class LunarLander extends JFrame {

private static JFrame window;

private static Graphics gr;

private static Image theBackground; 
private static Image theLander;     
private static Image theBang;      
private static Image theBottomFlame;
private static Image theLeftFlame;
private static Image theRightFlame;
private static Image theFlag;
private static Image theLandingSite;

private static int landerX=350, landerY=20; 
private static boolean explosion=false;   
private static int fuel=740; 

private static int landingY;  
private static boolean stop_moving=false; 

private static boolean fuel_stoped =  false;

public static void main(String[] args) {
    window = new JFrame();
    window.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    window.setLocation(550,10);
    window.setTitle("Houston, we have a Problem");
    window.setSize(1024,768);
    window.setResizable(false);

    BufferedImage canvas=new BufferedImage(1024,768,BufferedImage.TYPE_INT_ARGB);
    gr=canvas.getGraphics();
    JLabel label=new JLabel(new ImageIcon(canvas));
    window.add(label);

    window.setVisible(true);
    theBackground = GameImage.loadImage("Images//Background.jpg");
    theLander = GameImage.loadImage("Images//Rocket.png");
    theBang   = GameImage.loadImage("Images//explosion.gif");
    theBottomFlame  = GameImage.loadImage("Images//flamebottom.png");
    theLeftFlame  = GameImage.loadImage("Images//flameleft.png");
    theRightFlame  = GameImage.loadImage("Images//flameright.png");
    theFlag  = GameImage.loadImage("Images//flag.png");
    theLandingSite  = GameImage.loadImage("Images//site.png");

    GameKeyboard.initialise();

    ActionListener taskPerformer = new ActionListener()      
        {
            public void actionPerformed(ActionEvent evt)
            {
                doTimerAction();
            }
        };
    Timer t = new Timer(25, taskPerformer);
    t.start();

   }

static Random randomGenerator = new Random();
static int landingX = randomGenerator.nextInt(900);

private static boolean check_position(int x, int y){
    String CHECK="";
    if(y>485 && y<600){
        if(x>landingX-150 && x<landingX+20) {
            CHECK="TRUE";
            stop_moving = true;
        }
    }else{
        CHECK="FALSE";
    }
    if(CHECK=="TRUE"){
        return true;
    }else{
        return false;
    }
}

private static void doTimerAction() {

    gr.drawImage(theBackground, 0, 0, null);
    gr.drawImage(theLandingSite, landingX , landingY+670, null);
    char key= GameKeyboard.getKey();
    int  specialKey=GameKeyboard.getSpecialKey();




    gr.setColor( Color.orange ); 
    gr.setFont(new Font("Arial", Font.PLAIN, 16));
    gr.drawString("LEFT RIGHT UP and DOWN arrow keys to move", 10,80);
    gr.drawString("Key="+key+" specialKey="+specialKey ,10,100); 
    if (stop_moving == false){
        if(fuel_stoped==false){
            if (explosion == false) {


                switch (key) {

                    case 'W': landerY=landerY-3; --fuel; gr.drawImage(theBottomFlame, landerX+148, landerY+195, null); break;
                    case 'w': landerY=landerY-3; --fuel; gr.drawImage(theBottomFlame, landerX+148, landerY+195, null); break; 
                    case 'S': landerY=landerY+1;  break;
                    case 's': landerY=landerY+1;  break;
                    case 'A': landerX=landerX-1; --fuel; gr.drawImage(theRightFlame, landerX+189, landerY+83, null); break;
                    case 'a': landerX=landerX-1; --fuel; gr.drawImage(theRightFlame, landerX+189, landerY+83, null); break;
                    case 'D': landerX=landerX+1; --fuel; gr.drawImage(theLeftFlame, landerX+115, landerY+83, null); break;
                    case 'd': landerX=landerX+1; --fuel; gr.drawImage(theLeftFlame, landerX+115, landerY+83, null); break;
                    case 'Q': landerY=landerY-3;  landerX=landerX-2; gr.drawImage(theRightFlame, landerX+189, landerY+83, null);gr.drawImage(theBottomFlame, landerX+148, landerY+195, null); --fuel;break;
                    case 'q': landerY=landerY-3;  landerX=landerX-2; gr.drawImage(theRightFlame, landerX+189, landerY+83, null);gr.drawImage(theBottomFlame, landerX+148, landerY+195, null); --fuel; break;
                    case 'E': landerY=landerY-3;  landerX=landerX+2; gr.drawImage(theLeftFlame, landerX+115, landerY+83, null); gr.drawImage(theBottomFlame, landerX+148, landerY+195, null);  --fuel; break;
                    case 'e': landerY=landerY-3;  landerX=landerX+2; gr.drawImage(theLeftFlame, landerX+115, landerY+83, null); gr.drawImage(theBottomFlame, landerX+148, landerY+195, null);  --fuel; break;



                }


            }   
        }

             }


    // If the lander hasn't hit the ground yet, draw it and the rocket flame
    if(landerY < 550) {

        gr.drawImage(theLander, landerX, landerY, null);

    } 
    // If it is at the bottom draw and explosion again for a while, i.e. <400
    else if (landerY < 600) {
        gr.drawImage(theBang, landerX, landerY, null);
        gr.setFont(new Font("Arial", Font.BOLD, 40));
        gr.setColor( new Color(255, 100,100) ); 
        gr.drawString("GAME OVER", 400,400);
        explosion = true;
        //landerY = 560;

    } 

    if(check_position(landerX, landerY)) {
        gr.setFont(new Font("Arial", Font.BOLD, 40));
        gr.setColor( new Color(255, 100,100) ); 
        gr.drawString("Well Done", 400,400);
        gr.drawImage(theFlag, landingX+180 , landingY+540, null);
        stop_moving = true;

    }

   if(fuel<5){
    fuel_stoped= true;
       }

    // Example how to do non-image graphics, i.e. graphics that is created at runtime.
    // Here a fuel gauge ('fuel' is decreased by one every time this method is run.
    if(landerY < 550) {

        gr.setColor( new Color(200, 200, 200) ); //grey background
        gr.fillRect(1000, 0, 23, 800); 

        if(fuel>200)        gr.setColor( new Color(0, 255, 0) );    // green
        else if(fuel>100)   gr.setColor( new Color(255, 255, 0) );  // yellow
        else                gr.setColor( new Color(255, 0, 0) );    // red
        gr.fillRect(1003, 755-fuel, 16, fuel); 
    }

    window.repaint();       

} 

Answer 1

Well i haven't gone through the whole code but did notice one thing that you don't have any track of velocity.

well a simple tip to mimic gravity would be use a vector for position of object, velocity and gravity.

position.x=350; position.y=20;
velocity.x=0; velocity.y=0;
gravity.x=0; gravity.y=1; //depending on the strength of the gravity

//Update the position of object by adding velocity to it
position+=velocity;

//in case of keystrokes manipulate velocity rather that the position itself
case "w":velocity.y-=1;   //similarly for other cases

//constantly keep adding gravity to velocity
velocity+=gravity;

Hope you got the idea