android - How to write a switch statement inside a method -

i have 7 activities a.b,c,d,e,f,g. when click of these buttons, ex:if click a, want go activity. want in switch case using method. tried doing this,but app crashed:

what's wrong in code.y crashing?

package com.example.assignment2;  import android.content.intent; import android.os.bundle; import android.support.v7.app.actionbaractivity; import android.view.view; import android.widget.button; import android.widget.textview;  public class act_a extends actionbaractivity {     textview text;     button btn;     @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_activity_);         text = (textview) findviewbyid(r.id.display);         text.settext("this activity a");         text.settextsize(20);     }     public void display(view v) {         switch (btn.getid()) {         case r.id.buta:             intent intent = new intent(this, act_a.class);             startactivity(intent);             break;         case r.id.butb:             intent intent1 = new intent(this, act_b.class);             startactivity(intent1);             break;         case r.id.butc:             intent intent2 = new intent(this, act_c.class);             startactivity(intent2);             break;         case r.id.butd:             intent intent3 = new intent(this, act_d.class);             startactivity(intent3);             break;         case r.id.bute:             intent intent4 = new intent(this, act_e.class);             startactivity(intent4);             break;         case r.id.butf:             intent intent5 = new intent(this, act_f.class);             startactivity(intent5);             break;         case r.id.butg:             intent intent6 = new intent(this, act_g.class);             startactivity(intent6);             break;         }     }     public void nextactivity(view v) {         intent intent = new intent(this, act_b.class);         startactivity(intent);     } } 

public void display(view v) {     switch (btn.getid()) {  --------------  }  } 

change btn.getid() v.getid()

you trying access id of uninitialized object btn declared button btn.

do this

public class homeactivity extends actionbaractivity {  private textview text;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_home);     text = (textview) findviewbyid(r.id.display);     text.settext("this home activity");     text.settextsize(20); }  public void display(view v) {      intent mintent = null;     switch (v.getid()) {      case r.id.buta:         mintent = new intent(this, aboutactivity.class);         break;      case r.id.butb:         mintent = new intent(this, informationactivity.class);         break;      case r.id.butc:         mintent = new intent(this, contactactivity.class);         break;      case r.id.butd:         mintent = new intent(this, postsactivity.class);               break;     }      if(mintent != null){         startactivity(mintent);     //if wanted finish activity uncomment following line     //finish();     }  }   @override public void onbackpressed() {         super.onbackpressed(); }  } 

if wanted call activity , finish current activity should call finish method

intent mintent = new intent(homeactivity.this, aboutactivity.class); startactivity(mintent); finish(); 

if wanted finish current activity on button,

@override public void onbackpressed() {    //write functions need before finishing activity here // if written line **super.onbackpressed();** finish activity on press    super.onbackpressed(); }