Android BMI程式

package com.BMI;

import java.text.DecimalFormat;

import android.app.Activity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class BMIActivity extends Activity
{
    private EditText et_height=null;
    private EditText et_weight=null;
    private Button     bt_submit=null;
    private TextView tv_result=null;
    private Button      bt_exit=null;
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        
        et_height=(EditText)findViewById(R.id.et_height);
        et_weight=(EditText)findViewById(R.id.et_weight);
        bt_submit=(Button)findViewById(R.id.bt_submit);
        bt_exit=(Button)findViewById(R.id.bt_exit);
        tv_result=(TextView)findViewById(R.id.tv_result);
        
        bt_submit.setOnClickListener(listener);
        bt_exit.setOnClickListener(listener);

    }
    private OnClickListener listener = new OnClickListener()
    {
        public void onClick(View v)
        {
            Button button=(Button)v;
            double height=0;
            double weight=0;
            switch(button.getId())
            {
                case R.id.bt_submit:
                {
                    DecimalFormat nf=new DecimalFormat("0.00");
                    try
                    {
                        height=Double.parseDouble(et_height.getText().toString())/100;
                    } catch (Exception e)
                    {
                        height=1.65;
                    }
                    try
                    {
                        weight=Double.parseDouble(et_weight.getText().toString());    
                    } catch (Exception e)
                    {
                        weight=60;
                    }
                    System.out.println(height);
                    System.out.println(weight);

                    double BMI = weight/(height*height);
                    if(BMI>0)
                    {
                        tv_result.setText("Your BMI is "+nf.format(BMI));
                        if(BMI < 20)
                        {
                            Toast.makeText(BMIActivity.this, "Too light",Toast.LENGTH_LONG).show();
                        }
                        else if(BMI >25)
                        {
                            Toast.makeText(BMIActivity.this, "Too Weight",Toast.LENGTH_LONG).show();
                        }
                        break;
                    }
                    else
                    {
                        Toast.makeText(BMIActivity.this,"Input Error",Toast.LENGTH_LONG).show();
                        break;
                    }    

                }
                case R.id.bt_exit:
                {
                    System.exit(0);
                    break;
                }
            
            }
            
        }
    };
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
    <TextView  
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        android:text="身高(cm)"
        android:textColor="#f00"
        android:textStyle="bold"
        android:textSize="20sp"
        />
    <EditText
        android:id="@+id/et_height"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:numeric="integer"
        android:hint="165"
        />
    <TextView  
        android:layout_width="fill_parent" 
        android:layout_height="wrap_content" 
        android:text="体重(kg)"
        android:textColor="#f00"
        android:textStyle="bold"
        android:textSize="20sp"
        />
    <EditText
        android:id="@+id/et_weight"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:numeric="integer"
        android:hint="60"    
        />
    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        >
            <Button 
            android:id="@+id/bt_submit"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:textColor="#000"
            android:textStyle="bold"
            android:textSize="20sp"
            android:paddingLeft="10dp"
            android:paddingRight="10dp"
            android:text="计算 BMI 值"
        />
        <Button
            android:id="@+id/bt_exit"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_weight="1"
            android:textColor="#000"
            android:textStyle="bold"
            android:textSize="20sp"
            android:paddingLeft="10dp"
            android:paddingRight="10dp"
            android:text="退出"
        />
    
    </LinearLayout>

    <TextView 
        android:id="@+id/tv_result"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:textColor="#ff0"
        android:textSize="20sp"
        android:padding="20dp"
        />

</LinearLayout>