下面是纯Java代码实现流星划过天空的完整攻略。
步骤一：实现画布
首先需要使用Java的GUI库，比如Swing或JavaFX，来创建一个窗口，并在窗口上绘制流星。
使用JavaFX实现画布
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
public class MeteorShower extends Application {
private static final int CANVAS_WIDTH = 600;
private static final int CANVAS_HEIGHT = 400;
public void start(Stage primaryStage) throws Exception {
// Create a canvas
Canvas canvas = new Canvas(CANVAS_WIDTH, CANVAS_HEIGHT);
GraphicsContext gc = canvas.getGraphicsContext2D();
// Draw some background
gc.setFill(Color.BLACK);
gc.fillRect(0, 0, CANVAS_WIDTH, CANVAS_HEIGHT);
// Add canvas to a group and set up the scene
Group root = new Group();
root.getChildren().add(canvas);
Scene scene = new Scene(root, CANVAS_WIDTH, CANVAS_HEIGHT, Color.BLACK);
// Show the stage
primaryStage.setTitle("Meteor Shower");
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
在这个示例中，我们使用JavaFX库创建了一个600x400的画布，并且用黑色填充了整个画布。
步骤二：实现流星效果
接下来，我们需要实现流星的效果。我们可以用JavaFX中的AnimationTimer类来实现动画。
简单流星示例
以下是一个简单的流星示例，流星从左上角开始向右下角移动，然后消失在画布之外：
import javafx.animation.AnimationTimer;
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
public class MeteorShower extends Application {
private static final int CANVAS_WIDTH = 600;
private static final int CANVAS_HEIGHT = 400;
private static final Color[] colors = {Color.RED, Color.ORANGE, Color.YELLOW};
private double x = -50;
private double y = -50;
private int colorIdx = 0;
public void start(Stage primaryStage) throws Exception {
// Create a canvas
Canvas canvas = new Canvas(CANVAS_WIDTH, CANVAS_HEIGHT);
GraphicsContext gc = canvas.getGraphicsContext2D();
// Add canvas to a group and set up the scene
Group root = new Group();
root.getChildren().add(canvas);
Scene scene = new Scene(root, CANVAS_WIDTH, CANVAS_HEIGHT, Color.BLACK);
// Create an animation timer to update the meteor's position and draw it
AnimationTimer timer = new AnimationTimer() {
@Override
public void handle(long now) {
// Clear the canvas
gc.setFill(Color.BLACK);
gc.fillRect(0, 0, CANVAS_WIDTH, CANVAS_HEIGHT);
// Move the meteor
x += 5;
y += 5;
// Draw the meteor
gc.setFill(colors[colorIdx]);
gc.fillOval(x, y, 10, 10);
// Check if the meteor has gone off the screen
if (x > CANVAS_WIDTH || y > CANVAS_HEIGHT) {
x = -50;
y = -50;
colorIdx = (colorIdx + 1) % colors.length;
}
}
};
timer.start();
// Show the stage
primaryStage.setTitle("Meteor Shower");
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
}
在这个示例中，我们使用一个定时器来控制流星的位置和颜色。每个定时器的回调都会清除画布，然后将流星的位置向右下角移动，然后绘制一个彩色圆形。
更多流星示例
以上示例代码实现了基本的流星效果，但你可以按照需求进行更多的定制化开发，比如实现更真实的流星效果，或者让画布上存在多个同时运动的流星。
下面是另外一个示例，它实现了多个不同大小和速度的流星：
import javafx.animation.AnimationTimer;
import javafx.application.Application;
import javafx.scene.Group;
import javafx.scene.Scene;
import javafx.scene.canvas.Canvas;
import javafx.scene.canvas.GraphicsContext;
import javafx.scene.paint.Color;
import javafx.stage.Stage;
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class MeteorShower extends Application {
private static final int CANVAS_WIDTH = 600;
private static final int CANVAS_HEIGHT = 400;
private List<Meteor> meteors;
private Random random = new Random();
public void start(Stage primaryStage) throws Exception {
// Create a canvas
Canvas canvas = new Canvas(CANVAS_WIDTH, CANVAS_HEIGHT);
GraphicsContext gc = canvas.getGraphicsContext2D();
// Add canvas to a group and set up the scene
Group root = new Group();
root.getChildren().add(canvas);
Scene scene = new Scene(root, CANVAS_WIDTH, CANVAS_HEIGHT, Color.BLACK);
// Create some meteors
meteors = new ArrayList<>();
for (int i = 0; i < 50; i++) {
Meteor meteor = new Meteor();
meteor.x = random.nextInt(CANVAS_WIDTH);
meteor.y = random.nextInt(CANVAS_HEIGHT / 2);
meteor.size = random.nextInt(5) + 5;
meteor.speed = random.nextInt(10) + 5;
meteors.add(meteor);
}
// Create an animation timer to update the meteors' position and draw them
AnimationTimer timer = new AnimationTimer() {
@Override
public void handle(long now) {
// Clear the canvas
gc.setFill(Color.BLACK);
gc.fillRect(0, 0, CANVAS_WIDTH, CANVAS_HEIGHT);
// Update and draw the meteors
for (Meteor meteor : meteors) {
// Move the meteor
meteor.x += meteor.speed;
meteor.y += meteor.speed / 2;
// Draw the meteor
gc.setFill(meteor.color);
gc.fillOval(meteor.x, meteor.y, meteor.size, meteor.size);
// Check if the meteor has gone off the screen
if (meteor.x > CANVAS_WIDTH || meteor.y > CANVAS_HEIGHT) {
meteor.x = random.nextInt(CANVAS_WIDTH);
meteor.y = random.nextInt(CANVAS_HEIGHT / 2);
meteor.size = random.nextInt(5) + 5;
meteor.speed = random.nextInt(10) + 5;
meteor.color = Color.rgb(random.nextInt(255), random.nextInt(255), random.nextInt(255));
}
}
}
};
timer.start();
// Show the stage
primaryStage.setTitle("Meteor Shower");
primaryStage.setScene(scene);
primaryStage.show();
}
public static void main(String[] args) {
launch(args);
}
private static class Meteor {
public double x;
public double y;
public int size;
public int speed;
public Color color = Color.WHITE;
}
}
在这个示例中，我们创建了50个不同速度、颜色和大小的流星，然后使用定时器更新并绘制他们的位置。当流星飞出画布后，我们重新生成新的随机颜色、大小和速度，并在画布的新的位置开始移动。
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