java - Android init Array Problems -

i've been stucked find what's wrong code below.

here's mainactivity.java

package com.andri.hilltest;  import android.os.bundle; import android.app.activity; import android.view.menu; import android.view.view; import android.view.view.onclicklistener; import android.widget.button; import android.widget.edittext; import android.widget.toast;  public class mainactivity extends activity implements onclicklistener {      edittext txtplain, txtkey, txtcipher;     button btnencrypt;     string char_db = "abcdefghijklmnopqrstuvwxyzabc";     int array_angka[];     int i;      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);           txtplain = (edittext) findviewbyid(r.id.txtplain);         txtkey = (edittext) findviewbyid(r.id.txtkey);         txtcipher = (edittext) findviewbyid(r.id.txtcipher);          btnencrypt = (button) findviewbyid(r.id.btnencrypt);          btnencrypt.setonclicklistener(this);       }      @override     public void onclick(view v) {         if(v == btnencrypt){              string plaintextinput = txtplain.gettext().tostring();              char[] array_huruf = plaintextinput.tochararray();             //int[] angka2;               (i=0 ; < array_huruf.length ; i++){                  int posisi_huruf =  char_db.indexof(array_huruf[i]);                  toast.maketext(this, "tombol ditekan " +  posisi_huruf , toast.length_short).show();                 array_angka[i] = posisi_huruf; //if disable line code should run             }          }     }      @override     public boolean oncreateoptionsmenu(menu menu) {         // inflate menu; adds items action bar if present.         getmenuinflater().inflate(r.menu.main, menu);         return true;     }    } 

here's mainactivity.xml

<linearlayout      xmlns:android="http://schemas.android.com/apk/res/android"      android:layout_width="fill_parent"     android:layout_height="wrap_content"     android:orientation="vertical">     <textview          android:layout_width="fill_parent"         android:layout_height="wrap_content"         android:text="plaintext"         />     <edittext          android:layout_width="fill_parent"         android:layout_height="wrap_content"         android:id="@+id/txtplain"         android:hint="masukkan plaintext"         />     <textview          android:layout_width="fill_parent"         android:layout_height="wrap_content"         android:text="key"         />     <edittext          android:layout_width="fill_parent"         android:hint="masukkan key"         android:layout_height="wrap_content"         android:id="@+id/txtkey"         />     <button          android:layout_width="fill_parent"         android:layout_height="wrap_content"         android:text="encrypt"         android:id="@+id/btnencrypt"         />     <textview          android:layout_width="fill_parent"         android:layout_height="wrap_content"         android:text="cipher (hill cipher)"         />     <edittext          android:layout_width="fill_parent"         android:hint=""         android:layout_height="wrap_content"         android:id="@+id/txtcipher"         /> </linearlayout> 

the problem when put line of code insert value of int array loop. when ran , put string input, got error message

log.txt

04-11 10:50:22.039: d/androidruntime(17743): shutting down vm 04-11 10:50:22.039: w/dalvikvm(17743): threadid=1: thread exiting uncaught exception (group=0x40a621f8) 04-11 10:50:22.049: e/androidruntime(17743): fatal exception: main 04-11 10:50:22.049: e/androidruntime(17743): java.lang.nullpointerexception 04-11 10:50:22.049: e/androidruntime(17743):    @ com.andri.hilltest.mainactivity.onclick(mainactivity.java:52) 04-11 10:50:22.049: e/androidruntime(17743):    @ android.view.view.performclick(view.java:3511) 04-11 10:50:22.049: e/androidruntime(17743):    @ android.view.view$performclick.run(view.java:14105) 04-11 10:50:22.049: e/androidruntime(17743):    @ android.os.handler.handlecallback(handler.java:605) 04-11 10:50:22.049: e/androidruntime(17743):    @ android.os.handler.dispatchmessage(handler.java:92) 04-11 10:50:22.049: e/androidruntime(17743):    @ android.os.looper.loop(looper.java:137) 04-11 10:50:22.049: e/androidruntime(17743):    @ android.app.activitythread.main(activitythread.java:4609) 04-11 10:50:22.049: e/androidruntime(17743):    @ java.lang.reflect.method.invokenative(native method) 04-11 10:50:22.049: e/androidruntime(17743):    @ java.lang.reflect.method.invoke(method.java:511) 04-11 10:50:22.049: e/androidruntime(17743):    @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:789) 04-11 10:50:22.049: e/androidruntime(17743):    @ com.android.internal.os.zygoteinit.main(zygoteinit.java:556) 04-11 10:50:22.049: e/androidruntime(17743):    @ dalvik.system.nativestart.main(native method) 04-11 10:55:22.109: i/process(17743): sending signal. pid: 17743 sig: 9 

i don't know what's goin on code, hope out there solve problem. hope.... attention... terima kasih.

if not want specify length of array have use list...

arraylist<integer> array_angka = new arraylist<integer>(); 

you add follows

array_angka.add(posisi_huruf); 

you can retrieve arraylist follows

array_angka.get(0); 

remember if not know ahead of time length of array recreating entire array every time increase size of array, arraylist give dynamically growing array.