package com.example.bc67.myapplication;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;

    public void selfchange(View view) {
    }
        Button button_test = (Button)findViewById(R.id.button1);
        button_test.setText("Click Me !");
    }

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent"
    android:layout_height="match_parent" android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    android:paddingBottom="@dimen/activity_vertical_margin" tools:context=".MainActivity">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="New a Button"
        android:id="@+id/button1"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true"
        android:clickable="true"
        android:onClick="selfchange"/>
</RelativeLayout>