android 从零单排 第一期 按键显示helloworld

//java文件
package com.example.helloworld;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.view.TextureView;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.TextView;

public class MainActivity<Button> extends Activity {

    Button b;
    TextView t;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        b=(Button) this.findViewById(R.id.button1);
        t=(TextView) this.findViewById(R.id.textView1);
        
        ((View) b).setOnClickListener(new OnClickListener(){
            public void onClick(View v){
                t.setText("Hello World");
            }
        });

    }
}

<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:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="" />

    <Button
        android:id="@+id/button1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/textView1"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="134dp"
        android:text="来点我" />

</RelativeLayout>