通常輸入數值都會使用EditText等等的文字框當作對象, 如何才能很快速的從這些view取得數值呢？？
使用 getText().toString() 加上各個數值類別(Integer, Double, Float, Long, Byte, Short)的ParseXXX() 最快 如下

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;
public class GetValueFromTextView extends Activity
{
    private static final int PERCENT = 100;
    private static final int MONTH_COUNT = 12;
    private EditText mInput_lend;
    private EditText mInputRate;
    private EditText mInputNumber;
    private Button mSubmit;
    private TextView mAmount;
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        initComponents();
    }
    private void initComponents()
    {
        mInput_lend = (EditText) findViewById(R.id.input_lend);
        mInputNumber = (EditText) findViewById(R.id.input_number);
        mInputRate = (EditText) findViewById(R.id.input_rate);
        mSubmit = (Button) findViewById(R.id.submit);
        mSubmit.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v)
            {
                mAmount.setText("" + countAmount());
            }
        });
        mAmount = (TextView) findViewById(R.id.amount);
    }
    private double countAmount()
    {
        int lend = Integer.parseInt(mInput_lend.getText().toString());
        double rateOfMonth = Double.parseDouble(mInputRate.getText().toString()) / MONTH_COUNT
                / PERCENT;
        int number = Integer.parseInt(mInputNumber.getText().toString());
        return lend * (Math.pow(rateOfMonth + 1, number));
    }
}

重點在 countAmount 方法中, 以下列方式取得string並轉換成數字

int lend = Integer.parseInt(mInput_lend.getText().toString());
double rateOfMonth = Double.parseDouble(mInputRate.getText().toString()) / MONTH_COUNT / PERCENT;
int number = Integer.parseInt(mInputNumber.getText().toString());

但要小心轉型溢位的問題
main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >
    <TextView
        android:id="@+id/main_tv_title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/title"/>
    <TextView
        android:id="@+id/main_tv_lendHint"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/lend"/>
    <EditText
        android:id="@+id/input_lend"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:inputType="number"/>
    <TextView
        android:id="@+id/main_tv_rateHint"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/rate"/>
    <EditText
        android:id="@+id/input_rate"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:inputType="numberDecimal"/>
    <TextView
        android:id="@+id/main_tv_number"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/rate"/>
    <EditText
        android:id="@+id/input_number"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:inputType="number"/>
    <Button
        android:id="@+id/submit"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:text="@string/btn"/>
    <TextView
        android:id="@+id/amount"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"/>
</LinearLayout>

以及 strings.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string name="app_name">Count Round-amount savings</string>
    <string name="title">Round-amount savings:</string>
    <string name="lend">capital(NT$):</string>
    <string name="rate">rate of year(%):</string>
    <string name="number">number of periods:</string>
    <string name="btn">count</string>
</resources>