Question

public class HelloWorldActivity extends Activity 帮忙具体解释一下，新手，谢谢

public class HelloWorldActivity extends Activity {
/** Called when the activity is first created. */
private Button button;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
button = (Button)findViewById(R.id.btn);
button.setOnClickListener(new OnClickListener() {

public void onClick(View v) {
// TODO Auto-generated method stub
Toast.makeText(HelloWorldActivity.this, "hello", 3000).show();

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Answer 1

public class HelloWorldActivity extends Activity implements OnClickListener{
private Button button;
/*继承Activity，必须实现onCreate方法
* 每一个Activity都要在AndroidManifest.xml中注册，
* */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
button=(Button)findViewById(R.id.button);
button.setText("My Button");
button.setOnClickListener(this);
}