Java-Android
Posted 怪歌
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BasicsTwo（java）
反射
修改方法
public static void main(String[] args) throws ClassNotFoundException, NoSuchMethodException, InvocationTargetException, IllegalAccessException {
ArrayList<String> list = new ArrayList<>();
list.add("oiuoaisduf");
list.add("asljkdf");
Class<? extends ArrayList> aClass1 = list.getClass(); //通过对象名获取class
Class<ArrayList> aClass2 = ArrayList.class; //通过集合获取class
Class<?> aClass3 = Class.forName("java.util.ArrayList"); //通过包和类名获取class
Method add = aClass1.getDeclaredMethod("add", Object.class);
add.invoke(list,5.21345689756);
add.invoke(list,123456789);
add.invoke(list,5.21345689756);
System.out.println(list);
}
修改值
private static HashMap<String,User> map = new HashMap<>();
static {
User no1 = new User("wangyide", "5210");
User no2 = new User("aaa", "123");
map.put("user1",no1);
map.put("user2",no2);
}
public static void main(String[] args) {
Class<HashMap> hashMapClass = HashMap.class;
Collection<User> values = map.values();
Field[] declaredFields = hashMapClass.getDeclaredFields();
}
简易IO（面向文件的增删改查）
public class Demo {
private static Scanner scanner = new Scanner(System.in);
public static void main(String[] args) throws Exception {
start();
}
private static void start() throws Exception {
System.out.println("1.文件目录操作");
System.out.println("0.退出");
System.out.println("请输入您的选择：");
switch (scanner.nextInt())
{
case 1:
System.out.println("1:D:\\\\ 2.C:\\\\");
System.out.println("请选择路径");
File file = new File("D:\\\\");
File file1 = new File("C:\\\\");
if (scanner.nextInt()==2)
{
show(file1);
}else {
show(file);
}
start();
break;
case 0:
System.out.println("谢谢使用");
System.exit(0);
break;
default:
System.out.println("输入错误，请重新输入");
start();
break;
}
}
private static void show(File file1) throws Exception {
if (file1.isDirectory())
{
File[] files = file1.listFiles();
for (File s:
files) {
System.out.println(s.getName());
}
System.out.println("1.继续打开 2.创建文件 3.创建文件夹 4.删除文件或文件夹 5.返回上一级 0.退出");
int i = scanner.nextInt();
if (i==1)
{
System.out.println("请输入文件名：");
String name = scanner.next();
for (File s:
files) {
if (name.equals(s.getName()))
{
show(s);
}
}
}else if (i==2)
{
System.out.println("请输入文件名(加后缀名如：.txt)：");
String name = scanner.next();
File file = new File(file1+"/"+name);
file.createNewFile();
}else if (i==3)
{
System.out.println("请输入文件夹名：");
String name = scanner.next();
File file = new File(file1+"/"+name);
file.mkdir();
}else if (i==4)
{
System.out.println("请输入要删除的文件夹：");
String name = scanner.next();
File file6 = new File(file1+"/"+name);
deleteFile(file6);
System.out.println("删除成功");
}else if (i==0)
{
System.exit(0);
}else if (i==5)
{
String path = file1.getPath();
File parentFile = file1.getParentFile();
show(parentFile);
}
else {
System.out.println("输入错误");
}
}
}
private static void deleteFile(File file) {
if (file.exists())
{
if (file.isFile())
{
file.delete();
}else {
if (file.length()==0)
{
file.delete();
}
File[] files = file.listFiles();
for (File f:
files) {
if (f.isFile())
{
f.delete();
}else {
deleteFile(f);
}
}
file.delete();
}
}else {
System.out.println("不存在此文件");
}
}
}
IO流
缓冲流
缓冲流是用来优化字节或字符流的，
一般字符流比字节流读写要快，但字节流可读取写入除字符以外的数据
序列化流
序列化流可以读取或写入对象，但直接写入会造成乱码
转换流
转换流用来将字节流和字符流相互替换
一般读取JSON-url中的数据获取的流为字节流
一般编程会把字节流转换为字符流
加上缓冲流达到最佳效果
（文件字节输入流）FileInputStream
FileInputStream fileInputStream = new FileInputStream("字节流.txt");
byte[] bs = new byte[1024]; //用来存 读到的内容
int len = fileInputStream.read(bs); //len:读到的长度
String string = new String(bs,0,len);
System.out.println(string);
fileInputStream.close();
(文件字节输出流) FileOutputStream
FileOutputStream fileOutputStream = new FileOutputStream("字节流.txt");
fileOutputStream.write("你好".getBytes());
fileOutputStream.close();
(文件字符输入流)FileReader
FileReader fileReader = new FileReader("字符流.txt");
char[] cs = new char[1024]; //保存读到的内容
int len = fileReader.read(cs);
String string = new String(cs,0,len);
System.out.println(string);
fileReader.close();
(文件字符输出流)FileWriter
FileWriter fileWriter = new FileWriter("字符流.txt");
fileWriter.write("你好");
fileWriter.close();
【字节流复制(边读边写)】
//读
FileInputStream fileInputStream = new FileInputStream("D:\\\\install\\\\ideaIU-2020.1.3.exe");
//写
FileOutputStream fileOutputStream = new FileOutputStream("D:/aaa.exe");
byte[] bs = new byte[1024]; //存储读取到的内容
while (true) {
int len = fileInputStream.read(bs);
if (len==-1) {
break;
}
fileOutputStream.write(bs, 0, len);
}
fileInputStream.close();
fileOutputStream.close();
(缓冲输出字符流）BufferedWriter
FileWriter fileWriter = new FileWriter("缓冲字符流.txt");
BufferedWriter bufferedWriter = new BufferedWriter(fileWriter);
bufferedWriter.write("缓冲字符流,你好");
bufferedWriter.close();
(缓冲输入字符流) BufferedReader
FileReader fileReader = new FileReader("缓冲字符流.txt");
BufferedReader bufferedReader = new BufferedReader(fileReader);
// char[] cs = new char[1024];
//
// int len = bufferedReader.read(cs);
//
// String string = new String(cs, 0, len);
// System.out.println(string);
//特有的方法 读一行
// String readLine = bufferedReader.readLine();
// System.out.println(readLine);
//一般使用方法
String s = "";
StringBuffer stringbuffer = new StringBuffer();
while((s = bufferedReader.readLine())!=null){
stringbuffer.append(s);
}
System.out.println(stringbuffer.toString());
bufferedReader.close();
（字节字符转换流）
//写
FileOutputStream fileOutputStream = new FileOutputStream("转换流.txt");
OutputStreamWriter outputStreamWriter = new OutputStreamWriter(fileOutputStream , "UTF-8");
outputStreamWriter.write("转换流你好");
outputStreamWriter.close();
//读
FileInputStream fileInputStream = new FileInputStream("转换流.txt");
InputStreamReader inputStreamReader = new InputStreamReader(fileInputStream,"UTF-8");
char[] cs = new char[1024];
int len = inputStreamReader.read(cs);
String string = new String(cs, 0, len);
System.out.println(string);
inputStreamReader.close();
（序列化输入流）ObjectInputStream
FileInputStream fileInputStream = new FileInputStream("序列化流.txt");
ObjectInputStream objectInputStream = new ObjectInputStream(fileInputStream);
Student readObject = (Student) objectInputStream.readObject();
System.out.println(readObject);
objectInputStream.close();
（序列化输出流）ObjectOutputStream
FileOutputStream fileOutputStream = new FileOutputStream("序列化流.txt");
ObjectOutputStream objectOutputStream = new ObjectOutputStream(fileOutputStream);
Student student = new Student("张三");
objectOutputStream.writeObject(student);
objectOutputStream.close();
网络编程
简单群聊系统
Server类
服务类，用于循环获取客户端的连接，并创建每个连接客户端伴生的服务子线程类
public class Server {
//list用于存储连接中的Socket（存储在线好友）一般用HashMap存储
//再使用list存储User类
private static ArrayList<Socket> list = new ArrayList<>();
public static void main(String[] args) throws IOException {
ServerSocket serverSocket = new ServerSocket(37618);
System.out.println("等待连接中...........");
int i=0;
while (true)
{
Socket accept = serverSocket.accept();
list.add(accept);
System.out.println("连接成功");
new ServerThread(list,accept,i).start();
}
}
}
ServerThread类
public class ServerThread extends Thread{
private ArrayList<Socket> arrayList;
private Socket socket;
private int i;
public ServerThread(ArrayList<Socket> arrayList, Socket socket, int i) {
Java-Android