求大神帮忙

小弟已经调了一天也没有结果，求大神帮调
Java代码如下：
package com.calculate.editcalcu;
import android.app.Activity;
import android.os.Bundle;
import android.widget.EditText;
import android.widget.TextView;
public class MainActivity extends Activity {
private EditText calculateOne;
private EditText calculateTwo;
private EditText symbol;
private TextView display;
private float result;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
calculateOne=(EditText)findViewById(R.id.calculateOne);
calculateTwo=(EditText)findViewById(R.id.calculateTwo);
symbol=(EditText)findViewById(R.id.symbol);
display=(TextView)findViewById(R.id.display);
String calculatestr1=calculateOne.getText().toString();
String calculatestr2=calculateTwo.getText().toString();
String symbol1=symbol.getText().toString();
float calculate1=Float.parseFloat(calculatestr1);
float calculate2=Float.parseFloat(calculatestr2);
result=calculate1+calculate2;
char[] ch=symbol1.toCharArray();
char b=ch[0];
switch(b){
case '+': result=calculate1+calculate2;
break;
case '-': result=calculate1-calculate2;
break;
case '*': result=calculate1*calculate2;
break;
case '/': result=calculate1/calculate2;
break;
default : System.out.println("请重新输入符号");
}
String c=String.valueOf(result);
display.setText(c);
}
}
xml布局文件如下：
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<EditText
android:id="@+id/calculateOne"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
<EditText
android:id="@+id/symbol"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
<EditText
android:id="@+id/calculateTwo"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
<TextView
android:id="@+id/display"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
/>
</LinearLayout>