javaSE(17)(打印流、转换流、对象流、配置文件和递归)

打印流：
package zz.itheima.printstreamandobjectstream;

import java.io.PrintStream;
import java.io.PrintWriter;

public class TestPrintStream {

public static void main(String[] args) throws Exception{
//打印流
// 演示打印流PrintStream（字节打印流）和PrintWriter（字符打印流），官方推荐使用字符打印流
String s = "hello";
boolean b = true;
int age = 20;
double price = 19.8;
//把上面四个变量的值写到一个文本文件中
//用字节流
//write(int c)  write(byte[] b)
//用字符流
//write(int c) write(String s)

//用打印流PrintStream
/*public PrintStream(File file)
public PrintStream(String fileName)

public void flush()
public void close()
public void print(Xxx x)
pulic void println(Xxx x)*/
/*  PrintStream ps = new PrintStream("demo.txt");
ps.println(s);
ps.println(b);
ps.println(age);
ps.println(price);
ps.close();*/

//使用字符输出流
PrintWriter pw = new PrintWriter("demo.txt");
pw.println(s);
pw.println(b);
pw.println(age);
pw.println(price);
pw.close();
}

}
对象流：
package zz.itheima.printstreamandobjectstream;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class TestObjectStream {

public static void main(String[] args)throws Exception {
//对象流
/*ObjectOutputStream  对象序列化：把对象以流的形式写入文件
public ObjectOutputStream(OutputStream out)
public void close()
public void flush()
public final void writeObject(Object obj)*/
ObjectOutputStream oos = new ObjectOutputStream(new FileOutputStream("book.txt"));
oos.writeObject(new Book("aaa", 10));
oos.close();

/*ObjectInputStream 对象进行反序列化:以流的形式从文件中读取对象
public ObjectInputStream(InputStream in)
public void close()
public final Object readObject()*/
ObjectInputStream ois = new ObjectInputStream(new FileInputStream("book.txt"));
Book b = (Book)ois.readObject();
ois.close();
System.out.println(b.getName());
}

}
递归：
package zz.itheima.printstreamandobjectstream;

public class TestRecursion {

//递归
//递归就是方法自身调用自身，会产生类似循环的效果
//盗梦空间...（梦中梦）
//必须有条件出口，就是能退出方法的条件
//在控制台换行输出10次"java"，分别使用for和递归实现
public static void test1(){
for (int i = 0; i < 10; i++) {
System.out.println("java");
}
}
public static void test2(int n){
System.out.println("java");
if (n==0) {
return;
}
test2(--n);

}
public static void main(String[] args) {
test2(10);
}

}
输出指定目录下的所有文件：
package zz.itheima.printstreamandobjectstream;

import java.io.File;

public class TestRecursionDir {

// 输出指定目录下的所有文件(包括子文件夹)
public static void recursionDir(String path){
File f = new File(path);
String[] names = f.list();
for (int i = 0; i < names.length; i++) {
if (names[i].endsWith(".java")) {
System.out.println(names[i]);
File ziFile = new File(path+"\\"+names[i]);
if (ziFile.isDirectory()) {
recursionDir(path+"\\"+names[i]);

}
}
}

}
public static void main(String[] args) {
recursionDir("E:\\work");
}

}
向文本文件中写入对象：
package zz.itheima.printstreamandobjectstream;

import java.io.FileWriter;
import java.io.PrintWriter;

public class TestWriteObject {

public static void main(String[] args) throws Exception{
// 向文本文件中写入对象
//FileWriter
//write(int c)  write(String s)  write(char[] c)
FileWriter fw=new FileWriter("demo.txt");
fw.write(new Book("asdf",100).toString());
fw.close();

//PrintWriter
PrintWriter pw=new PrintWriter("book.txt");
pw.print(new Book("asdf",100));
pw.close();
}

}
属性配置文件：
package zz.itheima.printstreamandobjectstream;

import java.io.FileReader;
import java.io.PrintWriter;
import java.util.Properties;
import java.util.Set;

public class TestProperties {

public static void main(String[] args)throws Exception {
//属性配置文件，存储的是键值对
// 演示java.util.Properties

/*Properties p=new Properties();  //存储方式跟HashMap一样
p.put("a", "aa");
p.put("b", "aa");
p.put("c", "aa");
System.out.println(p);

HashMap hm=new HashMap();
hm.put("a", "aa");
hm.put("b", "aa");
hm.put("c", "aa");
System.out.println(hm);*/

/*      public Object setProperty(String key,String value)
public void list(PrintWriter out)
public void store(Writer writer, String comments)
public void load(Reader reader)
public String getProperty(String key)
public Set<String> stringPropertyNames()*/
Properties ps = new Properties();
ps.setProperty("阿发", "aa");
ps.setProperty("b", "aa");
ps.setProperty("c", "aa");

PrintWriter pw = new PrintWriter("demo.txt");
ps.list(pw);//把存储的键值对存储到文本文件中
pw.close();

//读取
ps.load(new FileReader("demo.txt"));//从文本文件中读取（加载）键值对
System.out.println(ps);
Set keys = ps.keySet();
for (Object key : keys) {
String value = (String) ps.get(key);
System.out.println(key+"="+value);

}

}

}
bean类：
package zz.itheima.printstreamandobjectstream;

import java.io.Serializable;

public class Book implements Serializable{
private static final long serialVersionUID = -3137157247111227006L;

private String name;
private int price;

public Book() {
super();
}

public Book(String name, int price) {
super();
this.name = name;
this.price = price;
}

public String getName() {
return name;
}

public void setName(String name) {
this.name = name;
}

public int getPrice() {
return price;
}

public void setPrice(int price) {
this.price = price;
}

/*  @Override
public String toString() {
return "Book [name=" + name + ", price=" + price + "]";
}*/
}
例子一：
package zz.itheima.printstreamandobjectstream;

import java.io.PrintWriter;
import java.util.Scanner;

public class Demo1 {

public static void main(String[] args)throws Exception  {
// 让用户在控制台录入学生的姓名、性别、年龄等信息，并使用PrintWriter写入到一个文本文件中
Scanner sc=new Scanner(System.in);
System.out.println("请输入姓名：");
String name=sc.next();
System.out.println("请输入性别：");
String sex=sc.next();
System.out.println("请输入年龄：");
int age=sc.nextInt();

PrintWriter pw=new PrintWriter("demo.txt");
pw.println(name);
pw.println(sex);
pw.println(age);
pw.close();
}

}
例子二：
package zz.itheima.printstreamandobjectstream;

import java.io.FileReader;
import java.io.PrintWriter;
import java.util.Properties;

public class Demo2 {

public static void main(String[] args) throws Exception{
// 使用Properties类结合IO流把身份证号和姓名这个键值对写到一个属性配置文件中，然后再读出来
Properties ps = new Properties();
ps.put("123", "zhangsan");
ps.put("456", "lisi");
ps.put("1789", "wangwu");
PrintWriter pw = new PrintWriter("demo.txt");
ps.list(pw);
pw.close();

ps.load(new FileReader("demo.txt"));//加载（读取文本文件中的键值对）
System.out.println(ps);
}

}
例子三：
package zz.itheima.printstreamandobjectstream;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;

public class Demo3 {

public static void main(String[] args)throws Exception {
// 创建一个Book类(书名，价格)，创建几个对象，然后实现序列化和反序列化
ObjectOutputStream oos=new ObjectOutputStream(new FileOutputStream("book.txt"));
oos.writeObject(new Book("aaa", 1000));
oos.writeObject(new Book("bbb", 1000));
oos.close();

ObjectInputStream ois =new ObjectInputStream(new FileInputStream("book.txt"));

while (true) {
try {
Book b=(Book)ois.readObject();
System.out.println(b.getName());
} catch (Exception e) {
break;
}

}

ois.close();
}

}