File file1 = new File(“c:\test\score.txt”); //創建File對象
//另一種File file1 = new File(“c:\test”,“socre.txt”);//拆成2個部分
//還一種先生成File file = new File(“c:\test”); File file1=new File(file,“socre.txt”);
System.out.println(“是否是目錄:”+file1.isDirectory());
System.out.println(“是否是文件:”+file1.isFile());
//創建文件
File file2 = new File(“c:\test”,“HashSet”);//創建文件目錄 先判斷是否創建
if(!file2.exists()){
file2.mkdir();
}
File file3 = new File(“c:\test\HashSet\Demo”);//創建多級文件目錄mkdirs()
if(!file3.exists()){
file3.mkdirs();
}
//創建文件
if(!file1.exists()){
file1.createNewFile(); //需要捕獲異常
}
字節流
InputStream字節輸入流 OutputStream字節輸出流
文件輸入流FileInputStream
public int read() 從輸入流中讀取一個數據字節
public int read(byte[] b) 從輸入流中將最多b.length個字節數據讀入一個byte數組中
public int read(byte[] b,int off,int len) 從輸入流中將最多len個字節的數據讀入byte數組中
public void close() 關閉此文件輸入流並釋放與此流有關的所有系統資源
案例1: 讀一個txt文件數據:
package com.test.file;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
public class FileInputDemo1 {
public static void main(String[] args) {
// TODO Auto-generated method stub
//創建一個FileputStream對象
try {
FileInputStream fis = new FileInputStream("test.txt");
int n = fis.read();
while(n!=-1) {
System.out.print((char)n);
n=fis.read();
}
fis.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
運行結果讀取出text.txt文件的數據
文件輸出流FileOutputStream
public void write(int b)
public void write(byte[] b)
public void write(byte[] b,int off,int len)
public void close()
案例2: 寫入數據並讀取:
package com.test.file;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class FileOutputDemo {
public static void main(String[] args) {
FileInputStream fis; //用於讀數據
try {
FileOutputStream fos = new FileOutputStream("test.txt");
//如果輸出FileOutputStream("test",true) 表示追加數據
try {
fos.write(50);
fos.write('a');
fis =new FileInputStream("test.txt");
System.out.println(fis.read());
System.out.println((char)fis.read());
fos.close();
fis.close();
} catch (IOException e) {
e.printStackTrace();
}
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
}
運行結果:
50
a
案例3: 複製文件 (保持文件大小相同):
package com.test.file;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class FileOutputDemo1 {
public static void main(String[] args) {
//文件拷貝
try {
FileInputStream fis = new FileInputStream("123.jpg");
FileOutputStream fos = new FileOutputStream("456.jpg");
int n=0;
byte[] b = new byte[1024];
//讀
while((n=fis.read(b))!=-1) {
fos.write(b,0,n); //這樣寫保持文件大小相同
}
fis.close();
fos.close();
} catch (FileNotFoundException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
}
}
緩衝流
緩衝輸入流BufferedInputStream
緩衝輸出流BufferedOutputStream
案例4:利用緩存方法
package com.test.file;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
public class BufferedDemo {
public static void main(String[] args) {
try {
FileOutputStream fos = new FileOutputStream("test.txt");
BufferedOutputStream bos = new BufferedOutputStream(fos);
FileInputStream fis = new FileInputStream("test.txt");
BufferedInputStream bis = new BufferedInputStream(fis);
long startTime = System.currentTimeMillis();//計算週期 開始時間
bos.write(50);
bos.write('a');
bos.flush();
System.out.println(bis.read());
System.out.println((char)bis.read());
long endTime = System.currentTimeMillis();
System.out.println(endTime-startTime);
fos.close();
bos.close();
fis.close();
bis.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
運行結果:
50
a
0
