Simple Runtime Error Unable to instantiate Activity

1package com.example.simplecalculator;
2
3import android.os.Bundle;
4import android.app.Activity;
5import android.view.Menu;
6import android.view.View;
7import android.widget.Button;
8import android.widget.EditText;
9
10public class MainActivity extends Activity {
11 int number;
12 int activityNumber;
13 EditText editText = (EditText) findViewById(R.id.editText1);
14 @Override
15 protected void onCreate(Bundle savedInstanceState) {
16 super.onCreate(savedInstanceState);
17 setContentView(R.layout.activity_main);
18 editText.setText(null);
19 Button Add = (Button) findViewById(R.id.bAdd);
20 Button Sub = (Button) findViewById(R.id.bSub);
21 Button Multi = (Button) findViewById(R.id.bMulti);
22 Button Divide = (Button) findViewById(R.id.bDivide);
23 Button Enter = (Button) findViewById(R.id.bEnter);
24 Enter.setOnClickListener(new View.OnClickListener() {
25
26 @Override
27 public void onClick(View v) {
28 int finalNumber = Integer.parseInt(editText.getText().toString());
29 if (activityNumber==1){
30 finalNumber = finalNumber + number;
31 }
32 else if (activityNumber ==2){
33 finalNumber = number - finalNumber;
34 }
35 else if (activityNumber ==3){
36 finalNumber = number * finalNumber;
37 }
38 else if (activityNumber==4){
39 finalNumber = number / finalNumber;
40 }
41 editText.setText(Integer.toString(finalNumber));
42 number = 0;
43 finalNumber = 0;
44 }
45 });
46 Add.setOnClickListener(new View.OnClickListener() {
47
48 @Override
49 public void onClick(View v) {
50 getTextInfo();
51 activityNumber=1;
52 }
53 });
54 Sub.setOnClickListener(new View.OnClickListener() {
55
56 @Override
57 public void onClick(View v) {
58 getTextInfo();
59 activityNumber = 2;
60 }
61 });
62 Multi.setOnClickListener(new View.OnClickListener() {
63
64 @Override
65 public void onClick(View v) {
66 getTextInfo();
67 activityNumber = 3;
68 }
69 });
70 Divide.setOnClickListener(new View.OnClickListener() {
71
72 @Override
73 public void onClick(View v) {
74 getTextInfo();
75 activityNumber=4;
76 }
77 });
78 }
79
80 @Override
81 public boolean onCreateOptionsMenu(Menu menu) {
82 // Inflate the menu; this adds items to the action bar if it is present.
83 getMenuInflater().inflate(R.menu.main, menu);
84 return true;
85 }
86 public void getTextInfo(){
87 number = Integer.parseInt((editText.getText().toString()));
88 editText.setText(null);
89 }
90
91}