Question

我是java的新手，所以如果有人能够解释它就会很棒。这也是在Android工作室顺便说一下。每当我尝试这样做时，我都会收到错误。

int next = 0;
public class Outlaw {
    String name;
    String message;
    public Outlaw(String name, String message){

    }
    public String getName(){
        return name;
    }
    public String getMessage(){
        return message;
    }



}

Outlaw outlaw0;
Outlaw outlaw1;
Outlaw outlaw2;
Outlaw outlaw3;
Outlaw outlaw4;
Outlaw outlaw5;
Outlaw outlaw6;
Outlaw outlaw7;
ArrayList<Outlaw> outlaws;


public void continueFunct(View view){
    Log.i("outlaws",outlaws.get(0).getMessage());
    if (step == 0){
        step =+ 1;
        infoTextView.setText(outlaws.get(0).getMessage());
    } else if (step == 1){

        show();
        next =+ 1;

    }

}

然后我在onCreate方法中有这个

 outlaws = new ArrayList<>();
    outlaw0 = new Outlaw("Trader Joe", "You caught Trader Joe selling faulty Lemons!");
    outlaw1 = new Outlaw("Dirty Dan", "\"No I'm Dirty Dan!\"");
    outlaw2 = new Outlaw("Itchy Trigger", "Well, Well, Well, if it isn't Itchy Trigger");
    outlaw3 = new Outlaw("Eye-Twitch Bill", "Agh! A monster! Oh never mind it's just Eye-Twitch Bill");
    outlaw4 = new Outlaw("Skinny Pete", "Sooo we meet again Skinny Pete");
    outlaw5 = new Outlaw("Whiskey Larry", "A drunken whiskey Larry stumbles into view");
    outlaw6 = new Outlaw("Alamo Jack", "A new challenger approaches! Alamo Jack!");
    outlaw7 = new Outlaw("El Loco", "\"That was my amigo! You will pay for what you have done!\"");
    outlaws.add(outlaw0);
    outlaws.add(outlaw1);
    outlaws.add(outlaw2);
    outlaws.add(outlaw3);
    outlaws.add(outlaw4);
    outlaws.add(outlaw5);
    outlaws.add(outlaw6);
    outlaws.add(outlaw7);

我知道我已经导入了所有的编写框架，但每次单击“继续”按钮时我都会收到错误。当我摆脱日志语句时，我试图设置的textView只是空白，使用Log语句应用程序崩溃。

这是我收到的错误消息，不知道该如何处理它可能会有所帮助。

05-26 20:44:08.826 21384-21384/com.scottolsonofficial.westventure E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.scottolsonofficial.westventure, PID: 21384
java.lang.IllegalStateException: Could not execute method for android:onClick
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:293)
    at android.view.View.performClick(View.java:5637)
    at android.view.View$PerformClick.run(View.java:22429)
    at android.os.Handler.handleCallback(Handler.java:751)
    at android.os.Handler.dispatchMessage(Handler.java:95)
    at android.os.Looper.loop(Looper.java:154)
    at android.app.ActivityThread.main(ActivityThread.java:6119)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
 Caused by: java.lang.reflect.InvocationTargetException
    at java.lang.reflect.Method.invoke(Native Method)
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288)
    at android.view.View.performClick(View.java:5637) 
    at android.view.View$PerformClick.run(View.java:22429) 
    at android.os.Handler.handleCallback(Handler.java:751) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6119) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) 
 Caused by: java.lang.NullPointerException: println needs a message
    at android.util.Log.println_native(Native Method)
    at android.util.Log.i(Log.java:164)
    at com.scottolsonofficial.westventure.MainActivity.continueFunct(MainActivity.java:106)
    at java.lang.reflect.Method.invoke(Native Method) 
    at android.support.v7.app.AppCompatViewInflater$DeclaredOnClickListener.onClick(AppCompatViewInflater.java:288) 
    at android.view.View.performClick(View.java:5637) 
    at android.view.View$PerformClick.run(View.java:22429) 
    at android.os.Handler.handleCallback(Handler.java:751) 
    at android.os.Handler.dispatchMessage(Handler.java:95) 
    at android.os.Looper.loop(Looper.java:154) 
    at android.app.ActivityThread.main(ActivityThread.java:6119) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Answer 1

您似乎忘记了分配班级的字段。

您的构造函数当前不执行任何操作，因此getMessage()会返回null，因为它从未被分配过。

public class Outlaw {
    private String name;
    private String message;
    public Outlaw(String name, String message){
        this.name = name;
        this.message = message;
    }
    public String getName(){
        return name;
    }
    public String getMessage(){
        return message;
    }
}

Answer 2

您的getMessage函数返回一个null对象。

您的代码的另一部分似乎是修改消息。我会将消息声明为

final String message;

这将确保代码中的otger部分无法使用它

Java：如何从arraylist中的对象调用方法

2 个答案: