Intent intent = new Intent(Intent.ACTION_SENDTO);
intent.setData(Uri.parse("mailto:"));//调用邮箱App

完成Just Java ——源码如下

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical"
        android:paddingBottom="@dimen/activity_vertical_margin"
        android:paddingLeft="@dimen/activity_horizontal_margin"
        android:paddingRight="@dimen/activity_horizontal_margin"
        android:paddingTop="@dimen/activity_vertical_margin"
        tools:context="com.example.clixin.justjava.MainActivity">

        <EditText
            android:id="@+id/name_edit_text"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:hint="@string/type_your_name_here"/>

        <TextView
            style="@style/CustomText"
            android:layout_marginBottom="16dp"
            android:text="@string/toppings"
             />

        <CheckBox
            android:id="@+id/whippied_cream_check_box"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:paddingLeft="16dp"
            android:text="@string/whippied_cream"
            android:textSize="16sp" />

        <CheckBox
            android:id="@+id/chocolate_check_box"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:paddingLeft="16dp"
            android:text="@string/chocolate"
            android:textSize="16sp" />

        <TextView
            style="@style/CustomText"
            android:layout_marginBottom="16dp"
            android:layout_marginTop="16dp"
            android:text="@string/quantity"
            />

        <LinearLayout
            android:layout_width="match_parent"
            android:layout_height="wrap_content">

            <Button
                android:layout_width="48dp"
                android:layout_height="48dp"
                android:layout_marginRight="8dp"
                android:onClick="decrement"
                android:text="@string/decrement" />

            <TextView
                android:id="@+id/quantity_text_view"
                android:layout_width="wrap_content"
                android:layout_height="wrap_content"
                android:text="@string/quantity_hint"
                android:textAppearance="?android:textAppearanceLarge" />

            <Button
                android:layout_width="48dp"
                android:layout_height="48dp"
                android:layout_marginLeft="8dp"
                android:onClick="increment"
                android:text="@string/increment" />

        </LinearLayout>


        <TextView
            style="@style/CustomText"
            android:layout_marginBottom="16dp"
            android:layout_marginTop="16dp"
            android:text="@string/order_summary"
             />

        <Button
            style="@style/CustomText"
            android:layout_marginTop="16dp"
            android:onClick="submitOrder"
            android:text="@string/order"
             />

    </LinearLayout>
</ScrollView>

Style.xml

<resources>

    <!-- Base application theme. -->
    <style name="AppTheme" parent="Theme.AppCompat.Light.DarkActionBar">
        <!-- Customize your theme here. -->
        <item name="colorPrimary">@color/colorPrimary</item>
        <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
        <item name="colorAccent">@color/colorAccent</item>
    </style>
    
    <style name="CustomText" >
        <item name="android:textAppearance">?android:textAppearanceLarge</item>
        <item name="android:textAllCaps">true</item>
        <item name="android:textColor">#344567</item>
        <item name="android:layout_width">wrap_content</item>
        <item name="android:layout_height">wrap_content</item>
    
    </style>

</resources>

String.xml

<resources>
    <string name="app_name">Just Java</string>
    <string name="type_your_name_here">Type your name here</string>
    <string name="toppings">Toppings</string>
    <string name="whippied_cream">Whippied Cream / 1￥</string>
    <string name="chocolate">chocolate / 2￥</string>
    <string name="quantity">Quantity</string>
    <string name="decrement">-</string>
    <string name="quantity_hint">1</string>
    <string name="increment">+</string>
    <string name="order_summary">Order Summary</string>
    <string name="price_hint">￥0</string>
    <string name="order">Order</string>
    <string name="order_summary_name">Name:</string>
    <string name="order_summary_whippied_cream">Has Whippied Cream?</string>
    <string name="order_summary_chocolate">Has Chocolate?</string>
    <string name="order_summary_total">total_price:</string>
    <string name="thank_you">Thank you!</string>
    <string name="order_summary_quantity">Quantity:</string>
    <string name="not_less_than_1">you can order at least 1 coffee</string>
    <string name="not_more_than_20">you can order at most 20 coffees</string>
    <string name="just_order_for">Just order for</string>
</resources>

MainActivity.java

package com.example.clixin.justjava;

import android.content.Intent;
import android.net.Uri;
import android.os.Bundle;
import android.provider.ContactsContract;
import android.support.v7.app.ActionBarActivity;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.CheckBox;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

import java.text.NumberFormat;

public class MainActivity extends AppCompatActivity {

    int quantity = 1;

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

    public void submitOrder(View view) {
        CheckBox whippiedCreamCheckBox = (CheckBox) findViewById(R.id.whippied_cream_check_box);
        boolean hasWhippiedCream = whippiedCreamCheckBox.isChecked();
        CheckBox chocolateCheckBox = (CheckBox) findViewById(R.id.chocolate_check_box);
        boolean hasChocolate = chocolateCheckBox.isChecked();
        EditText nameEditText = (EditText) findViewById(R.id.name_edit_text);
        String name = nameEditText.getText().toString();
        int price = calculatePrice(hasWhippiedCream, hasChocolate);
        String priceMassage = getOrderSummary(price, hasWhippiedCream, hasChocolate, name);

        Intent intent = new Intent(Intent.ACTION_SENDTO);
        intent.setData(Uri.parse("mailto:"));
        intent.putExtra(Intent.EXTRA_SUBJECT, getString(R.string.just_order_for) + name);
        intent.putExtra(Intent.EXTRA_TEXT, priceMassage);
        if(intent.resolveActivity(getPackageManager()) != null) {
            startActivity(intent);
        }

    }

    public void increment(View view) {

        if(quantity == 20) {
            Toast.makeText(this, getString(R.string.not_more_than_20), Toast.LENGTH_SHORT).show();
            return;
        }
        quantity = quantity + 1;
        display(quantity);

    }

    public void decrement(View view) {
        if(quantity == 1) {
            Toast.makeText(this, getString(R.string.not_less_than_1), Toast.LENGTH_SHORT).show();
            return;
        }
        quantity = quantity - 1;
        display(quantity);

    }

    private void display(int number) {
        TextView quantityTextView = (TextView) findViewById(R.id.quantity_text_view);
        quantityTextView.setText("" + number);
    }

    private int calculatePrice(boolean hasWippiedCream, boolean hasChocolate) {
        int basePrice = 5;

        if (hasWippiedCream) {
            basePrice += 1;
        }

        if (hasChocolate) {
            basePrice += 2;
        }
        return quantity * basePrice;
    }

    private String getOrderSummary(int price, boolean hasWhippiedCream, boolean hasChocolate, String name) {
        String summary = getString(R.string.order_summary_name) + name;
        summary += "\n" + getString(R.string.order_summary_quantity) + quantity;
        summary += "\n" + getString(R.string.order_summary_whippied_cream) + hasWhippiedCream;
        summary += "\n" + getString(R.string.order_summary_chocolate) + hasChocolate;
        summary += "\n" + getString(R.string.order_summary_total) + NumberFormat.getCurrencyInstance().format(price);
        summary += "\n" + getString(R.string.thank_you);
        return summary;
    }
}