planet.java

java编程的一些Applets例子。值得深入研究一下。

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// $Id: Planet.java,v 1.3 1996/04/16 20:55:23 greg Exp $

import java.awt.*;
import java.util.*;
import java.io.*;

public class Planet extends Figure
{
    Color bloo = new Color( 0, 128, 255 );
    Random rand;
    Figure friends[];
    int n_friends;
    TakesABullet tab = null;

    // For some reason a square is added to the world.
    Planet( TakesABullet tab, int lines[][][] ) {
	super( lines );
	rand = new Random();
	this.tab = tab;
	friends = new Figure[4];
	n_friends = 0;
	for (int i=0; i<n_lines; ++i)
	  addFriend( lines[i][0][0], lines[i][0][1],
		    lines[i][1][0], lines[i][1][1] );
    }

    // When resetting, remove all friends.
    public void reset() {
	n_friends = 0;
	super.reset();
    }

    // Add the given Figure as a Friend
    public void addFriend( Figure f ) {
	if (n_friends >= friends.length) {
	    Figure newFriends[] = new Figure[friends.length*2];
	    for (int i=0; i<friends.length; ++i)
	      newFriends[i] = friends[i];
	    friends = newFriends;
	}
	friends[n_friends++] = f;
    }

    // Add a Friend on the given line.
    public void addFriend( int sx, int sy, int ex, int ey ) {
	Figure f = Friend.onEdge( sx, sy, ex, ey );
	addFriend( f );
    }

    // Add a friend on the line indexed by the given number.
    public void addFriend( int which ) {
	addFriend( lines[which][0][0], lines[which][0][1],
		  lines[which][1][0], lines[which][1][1] );
    }

    // Remove the friend on the line indexed by the given number.
    public void removeFriend( int which ) {
	friends[which]=friends[--n_friends];
    }

    // Remove the friend on the line that is nearest (x,y).
    public void removeNearbyFriend( int x, int y ) {
	for (int i=0; i<n_friends; ++i) {
	    int dx = x - friends[i].lines[0][0][0];
	    int dy = y - friends[i].lines[0][0][1];
	    double d = Math.sqrt(dx*dx+dy*dy);
	    if (d < 10.0)
	      removeFriend( i );
	}
    }

    // Draw the world and its Friends.
    public void render( Graphics g ) {
	g.setColor( bloo );
	super.render( g );
	g.setColor( Color.red );
	renderFriends( g );
    }

    // Render all Friends
    public void renderFriends( Graphics g ) {
	for (int i=0; i<n_friends; ++i)
	  friends[i].render( g );
    }

    // The Friends sometimes fire bullets at the ship, whose position is
    // passed in.
    void fireBulletsMaybe( double num_buls, double shipx, double shipy ) {
	if (n_friends == 0) return;
	if (rand.nextDouble() < num_buls) {
	    int r = Math.abs( rand.nextInt() ) % n_friends;
	    Figure f = friends[r];
	    double v = Gravity.bul_vel/4;
	    int mx = f.lines[0][0][0];
	    int my = f.lines[0][0][1];
	    double dispx = mx-(f.lines[1][0][0]+f.lines[2][0][0])/2;
	    double dispy = my-(f.lines[1][0][1]+f.lines[2][0][1])/2;
	    double dx = shipx-mx;
	    double dy = shipy-my;
	    if (dx*dispx+dy*dispy < 0)
	      return;
	    mx += dispx/3;
	    my += dispy/3;
	    double dist = Math.sqrt( dx*dx + dy*dy );
	    tab.take( mx, my, v*dx/dist, v*dy/dist );
	}
    }

    // Intersect each of the friends with the given segment.
    public boolean intersectFriends( int b[][] ) {
	for (int i=0; i<n_friends; ++i)
	  if (friends[i].intersectLines( b )) {
	      removeFriend( i );
	      return true;
	  }
	return false;
    }

    // Read in the Friend positions as well.
    public void read( DataInputStream in ) throws IOException {
	super.read( in );
	int n = in.readInt();
	for (int i=0; i<n; ++i) {
	    Figure f = new Figure();
	    f.read( in );
	    addFriend( f );
	}
    }

    // Write out the Friend positions as well.
    public void write( DataOutputStream out ) throws IOException {
	super.write( out );
	out.writeInt( n_friends );
	for (int i=0; i<n_friends; ++i) {
	    friends[i].write( out );
	}
    }
}