I'm trying to create multiple projectiles, as if a spaceship is shooting an enemy.

catatau2001

MAIN CLASS:

int naveX, naveY;
int inimigoX, inimigoY;
Tiro [] tiros;

boolean tiroVisivel;
boolean naveDireita, naveEsquerda;

void setup(){
  size (800, 600);

  naveX = 375; naveY = height - 120;
  inimigoX = 385; inimigoY = 0;

  tiroVisivel = false;
  naveDireita = naveEsquerda = false; 

}

void draw(){
  background (0);

  nave();
  movimentoNave();
  if (tiroVisivel == true && tiros != null){
    for (int i = 0; i < tiros.length; i++){
      tiros[i].display();
      tiros[i].update();      
    }
  }

  inimigo();
}

void nave(){
  stroke (255);
  fill (255, 0, 0);
  rect (naveX, naveY, 50, 100);
}

void movimentoNave(){
  if (naveEsquerda == true && naveX > 0){
    naveX = naveX - 5;
  }
  if (naveDireita == true && naveX < width - 50){
    naveX = naveX + 5;
  }
}

void inimigo(){
  stroke (255);
  fill (0, 100, 255);
  rect (inimigoX, inimigoY, 30, 50);
}

void keyPressed(){
  if (key == ' '){
    append(tiros, new Tiro(naveX + 20, naveY - 30));
    tiroVisivel = true;
  }

  if(key == 'a' || key == 'A'){
    naveEsquerda = true;  
  }
  if(key == 'd' || key == 'D'){
    naveDireita = true;
  }

  if (key == 'r' || key == 'R'){
    setup();    
  }
}

void keyReleased(){
  if(key == 'a' || key == 'A'){
    naveEsquerda = false;  
  }
  if(key == 'd' || key == 'D'){
    naveDireita = false;
  }    
}

PROJECTILE CLASS:

public class Tiro {

  private int tiroX = naveX + 20;
  private int tiroY = naveY - 30;

  public Tiro(int x, int y){
    this.tiroX = x;
    this.tiroY = y;
  }


  void display(){
    stroke (255);
    fill (255, 0, 100);
    rect (tiroX, tiroY, 10, 20); 
  }

  void update(){
    if (tiroY > 0){
      tiroY = tiroY - 10;
    }
  }
}

---

Im using append on an empty array to create multiple projectiles, but every time I hit the spacebar Im getting a NullPointerException and I can't figure out why.

kfrajer

Please edit your post, select your code and hit ctrl+o to format your code. Make sure there is an empty line above and below your code

Kf

GoToLoop

Function append() creates a new clone of the passed array, plus the new element:
https://Processing.org/reference/append_.html

Given it doesn't directly mutate the original array, we need to re-assign its returned array back to the variable holding the former:
tiros = (Tiro[]) append(tiros, new Tiro(naveX + 20, naveY - 30));

P.S.: An ArrayList container is a much better fit for when the array's length constantly changes: *-:)
https://Processing.org/reference/ArrayList.html

kfrajer

Check the following code with discussed implementations. Notice that I changed your Tiro class and because of that change, you won't need the following variable declaration: tiroVisivel as far as I can see in your code.

Check for info: https://processing.org/reference/ArrayList.html

Kf

    int naveX, naveY;
    int inimigoX, inimigoY;
    ArrayList<Tiro> tiros;

    boolean tiroVisivel;
    boolean naveDireita, naveEsquerda;

    void setup() {
      size (800, 600);

      naveX = 375; 
      naveY = height - 120;
      inimigoX = 385; 
      inimigoY = 0;

      tiros=new ArrayList<Tiro>();

      tiroVisivel = false;
      naveDireita = naveEsquerda = false;
    }

    void draw() {
      background (0);

      nave();
      movimentoNave();
      if (tiroVisivel == true && tiros != null) {
        for (int i = 0; i < tiros.size(); i++) {
          tiros.get(i).display();
          tiros.get(i).update();
        }

        int nn = tiros.size();
        for (int i = nn; i >0; i--) {
          if (tiros.get(i-1).isAlive==false)
            tiros.remove(tiros.get(i-1));
        }
      }

      inimigo();
    }

    void nave() {
      stroke (255);
      fill (255, 0, 0);
      rect (naveX, naveY, 50, 100);
    }

    void movimentoNave() {
      if (naveEsquerda == true && naveX > 0) {
        naveX = naveX - 5;
      }
      if (naveDireita == true && naveX < width - 50) {
        naveX = naveX + 5;
      }
    }

    void inimigo() {
      stroke (255);
      fill (0, 100, 255);
      rect (inimigoX, inimigoY, 30, 50);
    }

    void keyPressed() {
      if (key == ' ') {
        tiros.add(new Tiro(naveX + 20, naveY - 30));
        tiroVisivel = true;
      }

      if (key == 'a' || key == 'A') {
        naveEsquerda = true;
      }
      if (key == 'd' || key == 'D') {
        naveDireita = true;
      }

      if (key == 'r' || key == 'R') {
        setup();
      }
    }

    void keyReleased() {
      if (key == 'a' || key == 'A') {
        naveEsquerda = false;
      }
      if (key == 'd' || key == 'D') {
        naveDireita = false;
      }
    }


    public class Tiro {

      private int tiroX = naveX + 20;
      private int tiroY = naveY - 30;
      private boolean isAlive;

      public Tiro(int x, int y) {
        this.tiroX = x;
        this.tiroY = y;
        isAlive=true;
      }


      void display() {
        stroke (255);
        fill (255, 0, 100);
        rect (tiroX, tiroY, 10, 20);
      }

      void update() {
        if (tiroY > 0) {
          tiroY = tiroY - 10;
        } else
          isAlive=false;
      }
    }