Button b1=(Button) findViewById(R.id.button1);
        b1.setOnClickListener(new OnClickListener() {			
			@Override
			public void onClick(View arg0) {
				// TODO Auto-generated method stub

				if("img.setImageResource(R.drawable.dow_000" !=null){
			    ImageView img = (ImageView) findViewById(R.id.imageView1);
			   img.setImageResource(R.drawable.dow_001);
				}
				else if("img.setImageResource(R.drawable.dow_001" != null)
				{
					 ImageView img = (ImageView) findViewById(R.id.imageView1);
				        img.setImageResource(R.drawable.dow_002);
				        
				}else if("img.setImageResource(R.drawable.dow_002" != null)
				{
					 ImageView img = (ImageView) findViewById(R.id.imageView1);
				        img.setImageResource(R.drawable.dow_003);
				}	 	
			}
		});