ArrayList question... that seems to be a challenge to many

Question

I have a tiny tiny problem that I seem incapable to solve by Googling.

I want to add Tabels (a class I made up) to an array. I tried below method in code and I also tried these variants

This: ArrayList<Tabeller> arrTabeller = new ArrayList<>(new Tabeller(1,true));
And this: arrTabeller.add(new Tabeller(1,true));

But as soon I try to add something, it crashes.

Questions:

why and why cant I see why in android studio?
How would you initialize and add an element to an array with class objects such as my table?

package com.example.mathstairs;

import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.Window;
import android.view.WindowManager;
import android.widget.Button;
import android.widget.FrameLayout;
import android.widget.RelativeLayout;
import android.widget.TextView;
import java.util.ArrayList;
import java.util.Collections;

public class MathStairMain extends Activity {

    FrameLayout gameFrame;
    RelativeLayout gameButtons; // Where I add the buttons

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN, WindowManager.LayoutParams.FLAG_FULLSCREEN);
        this.requestWindowFeature(Window.FEATURE_NO_TITLE);

        ArrayList<Tabeller> arrTabeller = new ArrayList<>();
        Tabeller e = new Tabeller(1,true);
        arrTabeller.add(e); // if commented away this program works, if active it is crashing
}

It is calling on the Tabel class

package com.example.mathstairs;

public class Tabeller {

    int tabell; // Tabeller som ska ingå
    Boolean use; // Sant eller falskt

    public Tabeller(int tabell, Boolean use)
    {
        this.tabell = tabell;
        this.use = use;
    }
}

And it works perfectly until I try to add.

   --------- beginning of crash
2022-05-13 10:54:14.044 1658-1658/? E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.mathstairs, PID: 1658
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.mathstairs/com.example.mathstairs.MathStairMain}: java.lang.IndexOutOfBoundsException: Index: 1, Size: 1
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3449)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
     Caused by: java.lang.IndexOutOfBoundsException: Index: 1, Size: 1
        at java.util.ArrayList.get(ArrayList.java:437)
        at com.example.mathstairs.MathStairMain.StartGame(MathStairMain.java:168)
        at com.example.mathstairs.MathStairMain.onCreate(MathStairMain.java:46)
        at android.app.Activity.performCreate(Activity.java:8000)
        at android.app.Activity.performCreate(Activity.java:7984)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1309)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3422)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601) 
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:223) 
        at android.app.ActivityThread.main(ActivityThread.java:7656) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) 
2022-05-13 10:54:14.095 1658-1658/? I/Process: Sending signal. PID: 1658 SIG: 9

Please provide a [mre]. The exception occurs in code you're not showing (MathStairMain.java, line 168). Your code is attempting to get the second item from a list with only 1 item (list indexes start at 0, not 1!) — Mark Rotteveel, May 13 '22 at 08:59
Caused by: java.lang.IndexOutOfBoundsException: Index: 1, Size: 1 at java.util.ArrayList.get(ArrayList.java:437) at com.example.mathstairs.MathStairMain.StartGame(MathStairMain.java:168) at com.example.mathstairs.MathStairMain.onCreate(MathStairMain.java:46) — Martin Marconcini, May 13 '22 at 09:02
Thank you @Mark Rotteveel! That might be it, I thougt a Array began at 1. — DPZonline, May 13 '22 at 09:09
You're using a List (ArrayList), not an array (though both use 0-based indexes). — Mark Rotteveel, May 13 '22 at 09:10

ArrayList question... that seems to be a challenge to many

0 Answers0