初学android，请问这是什么情况。。求指点！

Question

 package com.app.bangwoyi;

import android.support.v7.app.ActionBarActivity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;


public class MainActivity extends ActionBarActivity implements OnClickListener{

    private Button bt1,bt2,bt3,bt4;
    private TextView number1,number2,number3,number4;
    private int n1,n2,n3,n4;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        fun1();
    }

    private void fun1() {
        // TODO Auto-generated method stub

        bt1 = (Button) findViewById(R.id.bt1);
//      bt = (Button) findViewById(R.id.bt);        //语音
        bt2 = (Button) findViewById(R.id.bt2);
        bt3 = (Button) findViewById(R.id.bt3);
        bt4 = (Button) findViewById(R.id.bt4);
        bt1.setOnClickListener(this);
//      bt.setOnClickListener(this);
        bt2.setOnClickListener(this);
        bt3.setOnClickListener(this);
        bt4.setOnClickListener(this);
    }

        public void onClick(View v) {
            switch (v.getId()) {
            case R.id.bt1:
                n1++;
                number1.setText(String.valueOf(n1));
                break;

            case R.id.bt2:
                n2++;
                number2.setText(String.valueOf(n2));
                break;

            case R.id.bt3:
                n3++;
                number3.setText(String.valueOf(n3));
                break;

            case R.id.bt4:
                n4++;
                number4.setText(String.valueOf(n4));
                break;
            }
        }

}

Answer 1

MainActivity.java第45行抛出了空指针异常。

你看看你代码里：

 private TextView number1,number2,number3,number4;

声明之后全都没有赋值，就在switch...case里引用了，这必须得报错啊。