NullPointerException-音頻-2D Java Platformer

Question

我最近開始用Java進行編碼，並決定嘗試制作我從2D平台開始的游戲，並在網上找到一些音頻.java文件並將其添加到

但是，每當我運行游戲時，我都會收到NullPointerException，這真的使我煩惱，為什么它不起作用

這是我的音頻文件的代碼：

package me.EuanGraphics.Audio;

import javax.sound.sampled.AudioFormat;
import javax.sound.sampled.AudioInputStream;
import javax.sound.sampled.AudioSystem;
import javax.sound.sampled.Clip;

public class AudioPlayer {

private Clip clip;

public AudioPlayer(String s) {

    try {

        AudioInputStream ais =
                AudioSystem.getAudioInputStream(
                        getClass().getResourceAsStream(s)
                        );
        AudioFormat baseFormat = ais.getFormat();
        AudioFormat decodeFormat = new AudioFormat (
                AudioFormat.Encoding.PCM_SIGNED,
                baseFormat.getSampleRate(),
                16,
                baseFormat.getChannels(),
                baseFormat.getChannels() * 2,
                baseFormat.getSampleRate(), false
            );
            AudioInputStream dais = 
                    AudioSystem.getAudioInputStream(
                            decodeFormat, ais);
            clip = AudioSystem.getClip();
            clip.open(dais);


    }
    catch(Exception e) {
        e.printStackTrace();
    }

}

public void play() {
    if(clip == null) return;
    stop();
    clip.setFramePosition(0);
    clip.start();
}

public void stop() {
    if (clip.isRunning()) clip.stop();
}

public void close() {
    stop();
    clip.close();
}

}

這是我游戲中的菜單狀態，用於在選擇時調用音頻文件並播放

package me.EuanGraphics.GameState;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;

import javax.imageio.ImageIO;

import me.EuanGraphics.Entity.PlayerSave;
import me.EuanGraphics.Handler.Keys;
import me.EuanGraphics.Tilemap.Background;
import me.EuanGraphics.Audio.AudioPlayer;

public class MenuState extends GameState {

private BufferedImage head;
private Background menubg;
private AudioPlayer menuoption;
private AudioPlayer menuselect;

private int currentChoice = 0;
private String[] options = {
        "Start",
        "Quit"
};

private Color titleColor;
private Font titleFont;

private Font font;
private Font font2;

public MenuState(GameStateManager gsm) {
    super(gsm);

    try {

        //Load float head
        head = ImageIO.read(getClass().getResourceAsStream("/HUD/Hud.gif")).getSubimage(0, 12, 12, 11);
        menubg = new Background("/Backgrounds/Menu.png", 0);

        //Titles and fonts
        titleColor = Color.BLACK;
        titleFont = new Font("Time New Roman", Font.PLAIN, 20);
        font = new Font("Arial", Font.PLAIN, 14);
        font2 = new Font("Arial", Font.PLAIN, 10);


    }
    catch(Exception e) {
        e.printStackTrace();
    }
}


public void init() {

    menuoption = new AudioPlayer("/SFX/menuoption.wav");
    menuselect = new AudioPlayer("/SFX/menuselect.mp3");
}

public void update() {

    //Check Keys
    handleInput();

}


public void draw(Graphics2D g) {

    //Draw Background
    menubg.draw(g);

    // Draw Title
    g.setColor(titleColor);
    g.setFont(titleFont);
    g.drawString("Dragontale: Remastered", 55, 90);

    // Draw Menu Options
    g.setFont(font);
    g.setColor(Color.BLACK);
    g.drawString("Start", 145, 165);
    g.drawString("Quit", 145, 185);

    // Draw Floating Heads
    if(currentChoice == 0) g.drawImage(head, 125, 154, null);
    else if(currentChoice == 1) g.drawImage(head, 125, 174, null);

    //Other
    g.setFont(font2);
    g.drawString("2015 Euan P.", 10, 232);

}

private void select() {
    if(currentChoice == 0) {
        PlayerSave.init();
    }
    else if(currentChoice == 1) {
        System.exit(0);
    }
}

@Override
public void handleInput() {
    if(Keys.isPressed(Keys.ENTER)) select();
    if(Keys.isPressed(Keys.UP)) {
        if(currentChoice > 0) {
            menuoption.play();
            currentChoice--;
        }
    }
    if(Keys.isPressed(Keys.DOWN)) {
        if(currentChoice < options.length - 1) {
            menuoption.play();
            currentChoice++;
}
}
}
}

它在告訴代碼播放音頻文件EG menuoption.play（）的地方給了我一個錯誤。

謝謝-阮

Answer 1

當應用程序在需要對象的情況下嘗試使用null時，將產生NullPointerException。

也許在這里要做的事情：

 public void play() {
     if(clip == null) return;
     stop();
     clip.setFramePosition(0);
     clip.start(); }

http://docs.oracle.com/javase/7/docs/api/java/lang/NullPointerException.html

Answer 2

寫作：

private AudioPlayer menuoption;

等於

private AudioPlayer menuoption=null;

當您嘗試從= null的對象調用方法時，將收到NullPointerException。 因為您沒有在調用menuoption.play（）之前調用init（）（實際上，您並未在任何地方調用init（）），所以您正嘗試這樣做。 嘗試在MenuState的構造函數的末尾添加init（）。