我的安卓程序代码未启动并显示按摩"Unfortunately, "项目名称" has stopped"

我的android程序代码没有启动并显示消息"不幸的是，"projectname"已经停止"

我刚刚用android eclipse编写了我的第一个程序，但java代码中似乎有一个错误。有人能告诉我出了什么错吗？？

 package com.example.first;
 import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
 import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

public class MainActivity extends Activity implements OnClickListener{
private Button plus,minus ;
private TextView number;
@Override
protected void onCreate(Bundle savedInstanceState) {
    plus= (Button) findViewById(R.id.plus);
    minus=(Button) findViewById(R.id.minus);
    number= (TextView) findViewById(R.id.textView1);
    plus.setOnClickListener(this);
    minus.setOnClickListener(this);
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();
    if (id == R.id.action_settings) {
        return true;
    }
    return super.onOptionsItemSelected(item);
}
public void onClick(View v)
{
    if(v.getId() ==  R.id.plus)
    {
        number.setText("Plus");
    }
    else if(v.getId() ==  R.id.minus)
    {
        number.setText("Minus");
    }
}
}

super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
plus= (Button) findViewById(R.id.plus);
minus=(Button) findViewById(R.id.minus);
number= (TextView) findViewById(R.id.textView1);
...