I need help making my game restart ?

Can someone help me, i need to make it restart after the game has ended, basically draw the game from scratch every time i press a button(in my case Shift). Also any help on making enemies randomly appear for like 4-5 seconds and then disapear would be greatly appriciated. -Cheers

THE.CODE

//add power ups,random enemies spawn,confusion(reverse controls), border
snake sn;
food food1;
enemy enemy1;
int score;
PImage bkg;
PImage img;
PImage imgg;
boolean redo=true;
boolean stopgame=false;

void setup(){
    size(700, 500);
    frameRate(15);   
    sn = new snake();
    food1 = new food();
    enemy1 = new enemy();
    rectMode(CENTER);
    textAlign(CENTER, CENTER);
    bkg = loadImage("bkg.jpg");
    img = loadImage("gover.jpg");
    score =0;
    reset();
  }

void draw(){
  if(stopgame){    
    size(700, 500);
    background(img);
    noFill();
    rect(350, 390, 200, 100, 10);
    fill(0);
    textSize(18);
    text("Snake Lenght: "+sn.len+" ",350,378);
    textSize(15);
    text("To exit, press Esc.",350,420);
    return;
}
   else{
     playGame();
 }     
}

void playGame() {
    score = sn.len;
    stopgame=false; 
    background(bkg);
    drawScoreboard();
    sn.move();
    sn.display();
    food1.display();
    enemy1.display();

 if( dist(food1.xpos, food1.ypos, sn.xpos.get(0), sn.ypos.get(0)) < sn.slen ){
    food1.reset();
    sn.addLink();
    }

 if( dist(enemy1.xpos, enemy1.ypos, sn.xpos.get(0), sn.ypos.get(0)) < sn.slen ){
    enemy1.reset();
    sn.removeLink();

 }
}  

void reset() {
  playGame();
}

void drawScoreboard(){
  fill(250, 0, 250);
  textSize(25);
  text( "", width/2, 80);
  fill(250, 0, 250);
   textSize(20);
  text( "", width/2, 140);

  stroke(140, 140, 80);
  fill(255, 0 ,255);
  rect(0, 0, 0, 10);
  fill(18, 20, 67);
  textSize(25);
  text( "Score: " + (sn.len-1), 350, 255);
}

void keyPressed(){
  if(key == CODED){
    if(keyCode == LEFT && sn.dir!= "right"){
      sn.dir = "left";
    }
    if(keyCode == RIGHT && sn.dir!= "left"){
      sn.dir = "right";
    }
    if(keyCode == UP && sn.dir!= "down"){
      sn.dir = "up";
    }
    if(keyCode == DOWN && sn.dir!= "up"){
      sn.dir = "down";
    }
    if (keyCode == SHIFT) {
    playGame();
    }
    if (keyCode == ESC) {
    exit();
    } 

  }
}

class food{
  float xpos, ypos;
    food(){
    xpos = random(10, width - 10);
    ypos = random(10, height - 10);
  }

void display(){

   fill(154,  205  ,50);
   ellipse(xpos, ypos,21,21);
 }

void reset(){
    xpos = random(51, width - 51);
    ypos = random(51, height - 51);
 }   
}

class enemy{
  float xpos, ypos;
    enemy(){
    xpos = random(10, width - 10);
    ypos = random(10, height - 10);
  }

void display(){   
   fill(219,112,147);
   ellipse(xpos, ypos,21,21);
 }

void reset(){
    xpos = random(51, width - 51);
    ypos = random(51, height - 51);
 }   
}

class snake{
  int len;
  int len0;
  float slen;
  String dir; 
  ArrayList <Float> xpos, ypos;

  snake(){
    len = 1;
    slen = 20.5;
    xpos = new ArrayList();
    ypos = new ArrayList();
    xpos.add( random(width) );
    ypos.add( random(height) );
  }

void move(){
   for(int i = len - 1; i > 0; i = i -1 ){
    xpos.set(i, xpos.get(i - 1));
    ypos.set(i, ypos.get(i - 1));  
   } 
   if(dir == "left"){
     xpos.set(0, xpos.get(0) - slen);
   }
   if(dir == "right"){
     xpos.set(0, xpos.get(0) + slen);
   }

   if(dir == "up"){
     ypos.set(0, ypos.get(0) - slen);

   }

   if(dir == "down"){
     ypos.set(0, ypos.get(0) + slen);
   }
   xpos.set(0, (xpos.get(0) + width) % width);
   ypos.set(0, (ypos.get(0) + height) % height);

 // check if hit itself and if so cut off the tail
    if( checkHit() == true){
   stopgame=true;

    }
  }

void display(){
    for(int i = 0; i <len; i++){
      stroke(179, 140, 198);
      fill(99 , 184 , 255, map(i-1, 0, len-1, 250, 50));
      ellipse(xpos.get(i), ypos.get(i), slen, slen);
    }  
  }


void addLink(){
    xpos.add( xpos.get(len-1) + slen);
    ypos.add( ypos.get(len-1) + slen);
    len++;
  }

void removeLink(){
    xpos.remove( xpos.get(len-1) + slen);
    ypos.remove( ypos.get(len-1) + slen);
    len--;
    if (sn.len == 0){
    stopgame=true;
    }    
  }
   boolean checkHit(){
    for(int i = 1; i < len; i++){
     if( dist(xpos.get(0), ypos.get(0), xpos.get(i), ypos.get(i)) < slen){
       return true;
     }
    } 
    return false;
   } 
}