Enemy cant be hit?!?!?!

Question

My problem is that when the shot fired by the player "hits" the enemy, the enemy will not go away. I am making a Galaga like game and it is really confusing me as to why this isnt working. Any advice would be awesome!
He is my code:
//Main.java
import java.applet.*;
import java.awt.*;
import java.util.*;
public class Main extends Applet implements Runnable
     private Thread th;
     private Player player;
     private Shoot[] shot;
     private Enemy enemy;
     private int appletsize_x = 300;
     private int appletsize_y = 300;
     int enemySize = 15;
     boolean enemyHit;
     //Speed constants
     private int shotSpeed = -2;
     private int playerRightSpeed = 2;
     private int playerLeftSpeed = -2;
     private int enemySpeed = 1;
     //Player flags
     private boolean playerLeft;
     private boolean playerRight;
     //double buffering
     private Image dbImage;
     private Graphics dbg;
     public void init()
          player = new Player(150,280);
          shot = new Shoot[7]; //allows 7 shots to be fired at once
          enemy = new Enemy(150,125);
          enemy.setEnemySize(enemySize);
          setBackground(Color.black);
     public void start()
          th = new Thread(this);
          th.start();
     public void stop()
          th.stop();
     public void destroy()
          th.stop();
     public void run()
          Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
          while(true)
               //test for number of shots
               for(int i=0; i<shot.length; i++)
                    if (shot[i] != null)
                         shot.moveShot(shotSpeed);
//******************************************************************************************************I believe the probelm is here!!!********************************
                         if((shot[i].getX_Pos() == (enemy.getX_Pos()+20)) && (shot[i].getY_Pos() == (enemy.getY_Pos()+20)))
                         enemy.setEnemySize(0);
                         repaint();
                         shot[i] = null;
                         enemyHit = true;
                         if(shot[i].getY_Pos() < 0)
                              shot[i] = null;
                         }//end else if
                    }//end if
               }//end for
               //new enemies/targets
               if(enemyHit == false)
                    if (enemy.getX_Pos() > appletsize_x - enemySize)
                    // Change direction of enemy movement
                    enemySpeed = -1;
                    // enemy is bounced if its x - position reaches the left border of the applet
                    else if (enemy.getX_Pos() < 0)
                    // Change direction of enemy movement
                    enemySpeed = +1;
                    try
                         Thread.sleep(5);
                         enemy.moveEnemy(enemySpeed);
                    catch(Exception ex)
                    repaint();
               if(playerLeft)
                    player.moveX_Pos(playerLeftSpeed);
               if(playerRight)
                    player.moveX_Pos(playerRightSpeed);
               //repaint applet
               repaint();
               try
                    Thread.sleep(10);
               catch (InterruptedException ex)
                    //do nothing
               Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
     public boolean keyDown(Event e, int key)
          //Left key- moves player left
          if (key == Event.LEFT)
               playerLeft = true;
          //Right key - moves player right
          else if (key == Event.RIGHT)
               playerRight = true;
          //Space bar - fires shot
          else if(key == 32)
                         // generate new shot and add it to shots array
                         for(int i=0; i<shot.length; i++)
                              if(shot[i] == null)
                                   shot[i] = player.getShot();
                                   break;
          return true;
     }//end of keyDown
     //if fire is not being pressed do this
     public boolean keyUp(Event e, int key)
          if(key == Event.LEFT)
               playerLeft = false;
          else if(key == Event.RIGHT)
               playerRight = false;
          return true;
     public void update (Graphics g)
          if (dbImage == null)
               dbImage = createImage (this.getSize().width, this.getSize().height);
               dbg = dbImage.getGraphics ();
          dbg.setColor (getBackground ());
          dbg.fillRect (0, 0, this.getSize().width, this.getSize().height);
          dbg.setColor (getForeground());
          paint (dbg);
          g.drawImage (dbImage, 0, 0, this);
     }//end of update
     public void paint(Graphics g)
          player.drawPlayer(g);
          enemy.drawEnemy(g);
          //draw shots
          for(int i=0; i<shot.length;i++)
               if(shot[i] != null)
               shot[i].drawShot(g);
               }//end of inner if
          }//end of for
     }//end of paint
}//end of class

Answer 1

Here is the main class again and the enemy class. Please help!
//Main.java
import java.applet.*;
import java.awt.*;
import java.util.*;
public class Main extends Applet implements Runnable
     private Thread th;
     private Player player;
     private Shoot[] shot;
     private Enemy enemy;
     private int appletsize_x = 300;
     private int appletsize_y = 300;
     int enemySize = 15;
     boolean enemyHit;
     //Speed constants
     private int shotSpeed = -2;
     private int playerRightSpeed = 2;
     private int playerLeftSpeed = -2;
     private int enemySpeed = 1;
     //Player flags
     private boolean playerLeft;
     private boolean playerRight;
     //double buffering
     private Image dbImage;
     private Graphics dbg;
     public void init()
          player = new Player(150,280);
          shot = new Shoot[7];
          enemy = new Enemy(150,125);
          enemy.setEnemySize(enemySize);
          setBackground(Color.black);
     public void start()
          th = new Thread(this);
          th.start();
     public void stop()
          th.stop();
     public void destroy()
          th.stop();
     public void run()
          Thread.currentThread().setPriority(Thread.MIN_PRIORITY);
          while(true)
               //test for number of shots
               for(int i=0; i<shot.length; i++)
                    if (shot[i] != null)
                         shot.moveShot(shotSpeed);
//*********************I believe the probelm is here!!!********************************
                         if((shot[i].getX_Pos() == (enemy.getX_Pos()+100)) && (shot[i].getY_Pos() == (enemy.getX_Pos()-100))
                                   && (shot[i].getY_Pos() == (enemy.getY_Pos()-100)) && (shot[i].getY_Pos() == (enemy.getY_Pos()+100)))
                         //enemy.setEnemySize(0);
                         repaint();
                         shot[i] = null;
                         enemyHit = true;
                         if(shot[i].getY_Pos() < 0)
                              shot[i] = null;
                         }//end else if
                    }//end if
               }//end for
               //new enemies/targets
               if(enemyHit == false)
                    if (enemy.getX_Pos() > appletsize_x - enemySize)
                    // Change direction of enemy movement
                    enemySpeed = -1;
                    // enemy is bounced if its x - position reaches the left border of the applet
                    else if (enemy.getX_Pos() < 0)
                    // Change direction of enemy movement
                    enemySpeed = +1;
                    try
                         Thread.sleep(5);
                         enemy.moveEnemy(enemySpeed);
                    catch(Exception ex)
                    repaint();
               if(playerLeft)
                    player.moveX_Pos(playerLeftSpeed);
               if(playerRight)
                    player.moveX_Pos(playerRightSpeed);
               //repaint applet
               repaint();
               try
                    Thread.sleep(10);
               catch (InterruptedException ex)
                    //do nothing
               Thread.currentThread().setPriority(Thread.MAX_PRIORITY);
     public boolean keyDown(Event e, int key)
          //Left key- moves player left
          if (key == Event.LEFT)
               playerLeft = true;
          //Right key - moves player right
          else if (key == Event.RIGHT)
               playerRight = true;
          //Space bar - fires shot
          else if(key == 32)
                         // generate new shot and add it to shots array
                         for(int i=0; i<shot.length; i++)
                              if(shot[i] == null)
                                   shot[i] = player.getShot();
                                   break;
          return true;
     }//end of keyDown
     //if fire is not being pressed do this
     public boolean keyUp(Event e, int key)
          if(key == Event.LEFT)
               playerLeft = false;
          else if(key == Event.RIGHT)
               playerRight = false;
          return true;
     public void update (Graphics g)
          if (dbImage == null)
               dbImage = createImage (this.getSize().width, this.getSize().height);
               dbg = dbImage.getGraphics ();
          dbg.setColor (getBackground ());
          dbg.fillRect (0, 0, this.getSize().width, this.getSize().height);
          dbg.setColor (getForeground());
          paint (dbg);
          g.drawImage (dbImage, 0, 0, this);
     }//end of update
     public void paint(Graphics g)
          player.drawPlayer(g);
          if(enemyHit == false)
          enemy.drawEnemy(g, enemyHit);
          //draw shots
          for(int i=0; i<shot.length;i++)
               if(shot[i] != null)
               shot[i].drawShot(g);
               }//end of inner if
          }//end of for
     }//end of paint
}//end of class
Here is the Enemy class//Enemy.java
import java.awt.*;
import java.util.*;
public class Enemy
     private int x_pos;
     private int y_pos;
     private int radius;
     private int appletsize_x = 300;
     private int appletsize_y = 300;
     private int[] size = {10,15,12,8,9};
     //Constructor
     public Enemy(int x, int y)
          x_pos = x;
          y_pos = y;
     //Set the enemys size
     public void setEnemySize(int enemySize)
          radius = enemySize;
     //move the enemy left and right
     public void moveEnemy(int speed)
          x_pos += speed;
     //gets the y cords of the enemy
     public int getY_Pos()
          return y_pos;
     //gets the x cords of the enemy
     public int getX_Pos()
          return x_pos;
     //draw the enemy
     public void drawEnemy(Graphics g, boolean hit)
          if(hit == false)
               g.setColor(Color.white);
               g.fillOval(x_pos, y_pos, radius, radius);
}//close class