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public class MyApplication implements EntryPoint {  public void onModuleLoad() {    final Button button = new Button("Click me");    final Label label = new Label();    button.addClickListener(new ClickListener() {      public void onClick(Widget sender) {        if (label.getText().equals(""))          label.setText("Hello World!");        else           label.setText("");      }    });    RootPanel.get("slot1").add(button);    RootPanel.get("slot2").add(label);  }}