無效的索引3，大小爲2

Question

由於某種原因我得到這個錯誤，這裏是錯誤異常的縮短版本。我累了，以提供儘可能多的細節可能的，但我真的不知道該如何處理這個問題:(

09-16 19:39:18.404 15774-15774/com.spizer.mizer2 E/AndroidRuntime﹕ FATAL EXCEPTION: main 
Process: com.spizer.mizer2, PID: 15774 
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.spizer.mizer2/com.spizer.mizer2.DifficultyMenu}: java.lang.IndexOutOfBoundsException: Invalid index 3, size is 2 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2712) 
     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2777) 
     at android.app.ActivityThread.access$900(ActivityThread.java:179) 
     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1462) 
     at android.os.Handler.dispatchMessage(Handler.java:102) 
     at android.os.Looper.loop(Looper.java:145) 
     at android.app.ActivityThread.main(ActivityThread.java:5972) 
     at java.lang.reflect.Method.invoke(Native Method) 
     at java.lang.reflect.Method.invoke(Method.java:372) 
     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) 
     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) 
Caused by: java.lang.IndexOutOfBoundsException: Invalid index 3, size is 2 
     at java.util.ArrayList.throwIndexOutOfBoundsException(ArrayList.java:255) 
     at java.util.ArrayList.get(ArrayList.java:308) 
     at com.spizer.mizer2.DifficultyMenu.prepareListData(DifficultyMenu.java:187) 
     at com.spizer.mizer2.DifficultyMenu.onCreate(DifficultyMenu.java:43) 
     at android.app.Activity.performCreate(Activity.java:6295) 
     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1119) 
     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665) 
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2777) 
at android.app.ActivityThread.access$900(ActivityThread.java:179) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1462) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:145) 
at android.app.ActivityThread.main(ActivityThread.java:5972) 
at java.lang.reflect.Method.invoke(Native Method) 
at java.lang.reflect.Method.invoke(Method.java:372) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1399) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1194) 

和這裏是我的類

package com.spizer.mizer2; 

import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.view.Menu; 
import android.view.MenuItem; 
import android.widget.ExpandableListView; 

import java.util.ArrayList; 
import java.util.HashMap; 
import java.util.List; 
import android.view.View; 
import android.widget.ExpandableListView.OnChildClickListener; 
import android.widget.ExpandableListView.OnGroupClickListener; 
import android.widget.ExpandableListView.OnGroupCollapseListener; 
import android.widget.ExpandableListView.OnGroupExpandListener; 
import android.widget.Toast; 

public class DifficultyMenu extends AppCompatActivity { 

/** calls to make the class ProblemSelector usable in this class **/ 
ProblemSelector PS = new ProblemSelector(); 

private int T1; 
private int T2; 
private int T3; 
private int T4; 

ExpandableListAdapter listAdapter; 
ExpandableListView expListView; 
List<String> listDataHeader; 
HashMap<String, List<String>> listDataChild; 

@Override 
protected void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_difficulty_menu); 

    // get the list view 
    expListView = (ExpandableListView) findViewById(R.id.lvExp); 

    // preparing list data 
    prepareListData(); 

    listAdapter = new ExpandableListAdapter(this, listDataHeader, listDataChild); 

    // setting list adapter 
    expListView.setAdapter(listAdapter); 

    // List view Group click listener 
    expListView.setOnGroupClickListener(new OnGroupClickListener() { 
     @Override 
     public boolean onGroupClick(ExpandableListView parent, View v, 
            int groupPosition, long id) { 
      // Toast.makeText(getApplicationContext(), 
      // "Group Clicked " + listDataHeader.get(groupPosition), 
      // Toast.LENGTH_SHORT).show(); 
      return false; 
     } 
    }); 

    // List view Group expanded listener 
    expListView.setOnGroupExpandListener(new OnGroupExpandListener() { 
     @Override 
     public void onGroupExpand(int groupPosition) { 
      Toast.makeText(getApplicationContext(), 
        listDataHeader.get(groupPosition) + " Expanded", 
        Toast.LENGTH_SHORT).show(); 
     } 
    }); 

    // List view Group collapsed listener 
    expListView.setOnGroupCollapseListener(new OnGroupCollapseListener() { 
     @Override 
     public void onGroupCollapse(int groupPosition) { 
      Toast.makeText(getApplicationContext(), 
        listDataHeader.get(groupPosition) + " Collapsed", 
        Toast.LENGTH_SHORT).show(); 

     } 
    }); 

    // List view on child click listener 
    expListView.setOnChildClickListener(new OnChildClickListener() { 
     @Override 
     public boolean onChildClick(ExpandableListView parent, View v, 
            int groupPosition, int childPosition, long id) { 
      Toast.makeText(
        getApplicationContext(), 
        listDataHeader.get(groupPosition) 
          + " : " 
          + listDataChild.get(listDataHeader.get(groupPosition)).get(childPosition), Toast.LENGTH_SHORT) 
        .show(); 
      /** converts the selected number in the expandable list to a usable integer variable **/ 
      if(listDataHeader.get(groupPosition).equals("AdditionDifficulty")) { 
       String St1 = listDataHeader.get(childPosition); 
       int AddDiff = Integer.parseInt(St1); 
      } 
      else if(listDataHeader.get(groupPosition).equals("SubtractionDifficulty")) { 
       String St2 = listDataHeader.get(childPosition); 
       int SubDiff = Integer.parseInt(St2); 
      } 
      else if(listDataHeader.get(groupPosition).equals("MultiplicationDifficulty")) { 
       String St3 = listDataHeader.get(childPosition); 
       int MultiDIff = Integer.parseInt(St3); 
      } 
      else if(listDataHeader.get(groupPosition).equals("DivisionDifficulty")) { 
       String St4 = listDataHeader.get(childPosition); 
       int DivisDiff = Integer.parseInt(St4); 
      } 
//    else { 
//     /** public static int e("DifficultyMenu.class", "could  not parse a group position when user selected a field"); **/ 
//    } 
      return false; 
     } 
    }); 
} 

/* 
* Preparing the list data 
*/ 
private void prepareListData() { 
    listDataHeader = new ArrayList<>(); 
    listDataChild = new HashMap<>(); 

    // Adding child data 
    if(PS.AddProb) { listDataHeader.add("AdditionDifficulty"); } 
    if(PS.SubProb) { listDataHeader.add("SubtractionDifficulty"); } 
    if(PS.MultiProb) { listDataHeader.add("MultiplicationDifficulty"); } 
    if(PS.DivisProb) { listDataHeader.add("DivisionDifficulty"); } 

    /** this removes fields that the user has not selected to practice **/ 
    if(!PS.AddProb) { listDataHeader.remove("AdditionDifficulty"); } 
    if(!PS.SubProb) { listDataHeader.remove("SubtractionDifficulty"); } 
    if(!PS.MultiProb) { listDataHeader.remove("MultiplicationDifficulty"); } 
    if(!PS.DivisProb) { listDataHeader.remove("DivisionDifficulty"); } 

    // Adding child data 
    List<String> AdditionDifficulty = new ArrayList<>(); 
    while (true) { 
     if (T1 < 21) { 
      String S1 = Integer.toString(T1); 
      AdditionDifficulty.add(S1); 
      T1++; 
     } else { 
      break; 
     } 
    } 

    List<String> SubtractionDifficulty = new ArrayList<>(); 
    while (true) { 
     if (T2 < 21) { 
      String S2 = Integer.toString(T2); 
      SubtractionDifficulty.add(S2); 
      T2++; 
     } else { 
      break; 
     } 
    } 

    List<String> MultiplicationDifficulty = new ArrayList<>(); 
    while (true) { 
     if (T3 < 21) { 
      String S3 = Integer.toString(T3); 
      MultiplicationDifficulty.add(S3); 
      T3++; 
     } else { 
      break; 
     } 
    } 

    List<String> DivisionDifficulty = new ArrayList<>(); 
    while (true) { 
     if (T4 < 21) { 
      String S4 = Integer.toString(T4); 
      DivisionDifficulty.add(S4); 
      T4++; 
     } else { 
      break; 
     } 
    } 

    /** this draws out the Expandable lists **/ 
    if(PS.AddProb) { listDataChild.put(listDataHeader.get(0), AdditionDifficulty); } 
    if(PS.SubProb) { listDataChild.put(listDataHeader.get(1), SubtractionDifficulty); } 
    if(PS.MultiProb) { listDataChild.put(listDataHeader.get(2), MultiplicationDifficulty); } 
    if(PS.DivisProb) { listDataChild.put(listDataHeader.get(3), DivisionDifficulty); } 
} 

@Override 
public boolean onCreateOptionsMenu(Menu menu) { 
    // Inflate the menu; this adds items to the action bar if it is present. 
    getMenuInflater().inflate(R.menu.menu_difficulty_menu, menu); 
    return true; 
} 

@Override 
public boolean onOptionsItemSelected(MenuItem item) { 
    // Handle action bar item clicks here. The action bar will 
    // automatically handle clicks on the Home/Up button, so long 
    // as you specify a parent activity in AndroidManifest.xml. 
    int id = item.getItemId(); 

    //noinspection SimplifiableIfStatement 
    if (id == R.id.action_settings) { 
     return true; 
    } 

    return super.onOptionsItemSelected(item); 
} 

}

代碼

Answer 1

這是一個註釋，不是一個答案，但我想格式化代碼

是不是這樣：

while (true) { 
    if (T1 < 21) { 
     String S1 = Integer.toString(T1); 
     AdditionDifficulty.add(S1); 
     T1++; 
    } else { 
     break; 
    } 
} 

更好地寫成這樣：

for (; T1 < 21; T1++) { 
    AdditionDifficulty.add(Integer.toString(T1)); 
} 

不知道爲什麼T1是一個領域，因爲這永遠使用它是這個代碼的唯一代碼。

另請注意，字段名稱應在camelCase。

所以，如果你刪除該字段T1，代碼變爲：

for (int i = 0; i < 21; i++) { 
    AdditionDifficulty.add(Integer.toString(i)); 
}