SJ64 认识字符串，完善JUST JAVA

布局层次草图

String

字符串常量，与int一样

数据类型 + 变量名 = 变量值;

String priceMassage = "Free";

需要注意的是，String值由两个双引号包围着

如果需要使用双引号，则要用转义字符\" 将双引号转义，如

String priceMassage = "She said \"1 dollar\"";

\n 是换行的转义字符

字符串的连接

使用 + 来连接，如

String priceMassage = "Amount Due" + "￥10";

如果将字符串和整形数字连接起来会生成一个新的字符串，如
String priceMassage = "￥" + 100;

JUST JAVA JUST JAVA

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
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">

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="16dp"
    android:text="Quantity"
    android:textAllCaps="true"
    android:textAppearance="?android:textAppearanceLarge"
    android:textColor="#344567" />

<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content">
    <Button
        android:layout_width="48dp"
        android:layout_height="48dp"
        android:text="-"
        android:layout_marginRight="8dp"
        android:onClick="decrement"/>

    <TextView
        android:id="@+id/quantity_text_view"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="0"
        android:textAppearance="?android:textAppearanceLarge" />

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

</LinearLayout>


<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginBottom="16dp"
    android:layout_marginTop="16dp"
    android:text="Price"
    android:textAllCaps="true"
    android:textAppearance="?android:textAppearanceLarge"
    android:textColor="#344567" />

<TextView
    android:id="@+id/price_text_view"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="￥0.0"
    android:textAppearance="?android:textAppearanceLarge" />

<Button
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_marginTop="16dp"
    android:text="Order"
    android:textAllCaps="true"
    android:textAppearance="?android:textAppearanceLarge"
    android:onClick="submitOrder"/>

</LinearLayout>

MainActivity.java

package com.example.clixin.justjava;

import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.widget.TextView;

import java.text.NumberFormat;

public class MainActivity extends ActionBarActivity {

    int quantity = 0;

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

    public void submitOrder(View view) {
        int price = quantity * 5;
        String priceMassage = "Total: ￥" + price;
        priceMassage = priceMassage + "\nThank you!";
        displayMassage(priceMassage);
    }

    public void increment(View view) {
        quantity = quantity + 1;
        display(quantity);

    }

    public void decrement(View view) {
        quantity = quantity - 1;
        display(quantity);

    }

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

    private void displayPrice(int number) {
        TextView priceTextView = (TextView)findViewById(R.id.price_text_view);
        priceTextView.setText(NumberFormat.getCurrencyInstance().format(number));
    }

    private void displayMassage(String massage) {
        TextView priceTextView = (TextView)findViewById(R.id.price_text_view);
        priceTextView.setText(massage);
    }
}