tumbleweed.java

一个j2me的手机程序

第六章


Listing 6. Tumbleweed.java 

package net.frog_parrot.jump;

import java.util.Random;

import javax.microedition.lcdui.*;
import javax.microedition.lcdui.game.*;

/**
* This class represents the tumbleweeds that the player
* must jump over.
*
* @author Carol Hamer
*/
public class Tumbleweed extends Sprite {

//---------------------------------------------------------
// Dimension fields
/**
* The width of the tumbleweed's bounding square.
*/
static final int WIDTH = 16;

//---------------------------------------------------------
// Instance fields

/**
* Random number generator to randomly decide when to appear.
*/
private Random myRandom = new Random();

/**
* Whether this tumbleweed has been jumped over.
* This is used to calculate the score.
*/
private boolean myJumpedOver;

/**
* Whether this tumbleweed enters from the left.
*/
private boolean myLeft;

/**
* The Y coordinate of the tumbleweed.
*/
private int myY;

//---------------------------------------------------------
// Initialization

/**
* Constructor initializes the image and animation.
* @param left Whether this tumbleweed enters from the left.
*/

　public Tumbleweed(boolean left) throws Exception {
　　super(Image.createImage("/images/tumbleweed.png"), WIDTH, WIDTH);
　　myY = JumpManager.DISP_HEIGHT - WIDTH - 2;
　　myLeft = left;
　　if(!myLeft) {
　　　setTransform(TRANS_MIRROR);
　　}
　　myJumpedOver = false;
　　setVisible(false);
　}

　//---------------------------------------------------------
　// Graphics

　/**
　* Move the tumbleweed back to its initial (inactive) state.
　*/
　void reset() {
　　setVisible(false);
　　myJumpedOver = false;
　}

　/**
　* Alter the tumbleweed image appropriately for this frame.
　* @param left Whether the player is moving left
　* @return How much the score should change by after this
　* advance.
　*/
　int advance(Cowboy cowboy, int tickCount, boolean left, int currentLeftBound, int currentRightBound) {
　　int retVal = 0;
　　// If the tumbleweed goes outside of the display
　　// region, set it to invisible since it is
　　// no longer in use.
　　if((getRefPixelX() + WIDTH <= currentLeftBound) || (getRefPixelX() - WIDTH >= currentRightBound)) {
　　　setVisible(false);
　　}
　　// If the tumbleweed is no longer in use (i.e., invisible)
　　// it is given a 1 in 100 chance (per game loop)
　　// of coming back into play:
　　if(!isVisible()) {
　　　int rand = getRandomInt(100);
　　　if(rand == 3) {
　　　　// When the tumbleweed comes back into play,
　　　　// you reset the values to what they should
　　　　// be in the active state:
　　　　myJumpedOver = false;
　　　　setVisible(true);
　　　　// Set the tumbleweed's position to the point
　　　　// where it just barely appears on the screen
　　　　// so that it can start approaching the cowboy:
　　　　if(myLeft) {
　　　　　setRefPixelPosition(currentRightBound, myY);
　　　　　move(-1, 0);
　　　　} else {
　　　　　setRefPixelPosition(currentLeftBound, myY);
　　　　　move(1, 0);
　　　　}
　　　}
　　　} else {
　　　　// When the tumbleweed is active, you advance the
　　　　// rolling animation to the next frame and then
　　　　// move the tumbleweed in the right direction across
　　　　// the screen.
　　　　if(tickCount % 2 == 0) { // Slow the animation down a little. nextFrame();
　　　}
　　　if(myLeft) {
　　　　move(-3, 0);
　　　　// If the cowboy just passed the tumbleweed
　　　　// (without colliding with it), you increase the
　　　　// cowboy's score and set myJumpedOver to true
　　　　// so that no further points will be awarded
　　　　// for this tumbleweed until it goes off the screen
　　　　// and then is later reactivated:
　　　　if((! myJumpedOver) && (getRefPixelX() < cowboy.getRefPixelX())) {
　　　　　myJumpedOver = true;
　　　　　retVal = cowboy.increaseScoreThisJump();
　　　　}
　　　　} else {
　　　　　move(3, 0);
　　　　　if((! myJumpedOver) && (getRefPixelX() > cowboy.getRefPixelX() + Cowboy.WIDTH)) {
　　　　　　myJumpedOver = true;
　　　　　　retVal = cowboy.increaseScoreThisJump();
　　　　　}
　　　　}
　　　}
　　　return(retVal);
　　}

　　/**
　　* Gets a random int between
　　* zero and the param upper.
　　*/
　　public int getRandomInt(int upper) {
　　　int retVal = myRandom.nextInt() % upper;
　　　if(retVal < 0) {
　　　　retVal += upper;
　　　}
　　　return(retVal);
　　}

　}