FileInputStream类是InputStream类的子类，称为文件字节输入流。按字节读取文件中的数据。
构造方法：FileInputStream(String name)
FileInputStream(File file)
读取文件并输出：
public void test() throws IOException{
File file = new File("hello.txt");
FileInputStream in = null;
try{
in = new FileInputStream(file);
int a = in.read();
String str = new String();
while(a != -1){
str += (char)a;
a = in.read();
}
System.out.println(str);
}catch(IOException e){
System.out.println(e);
}
}
输出结果为：文件hello.txt中的内容。
FileOutputStream类是OutputStream类的子类，称为文件字节输出流。提供基本的文件按字节写入能力。
构造方法：FileOutputStream(String name)
FileOutputStream(File file)
写入文件并输出：
public void test1(){
File file = new File("hello.txt");
byte b[] = "Welcome to read my blog！".getBytes();//字符串中的内容为将写入的内容，需调用getBytes()函数转换为字节形式
FileOutputStream out = null;
FileInputStream in = null;
try{
out = new FileOutputStream(file);
out.write(b);
out.flush();
in = new FileInputStream(file);
int n = 0;
while((n = in.read(b, 0, 1)) != -1){
String str = new String(b,0,n);
System.out.println(str);
}
}catch(IOException e){
System.out.println(e);
}
finally{
try{
out.close();
}catch(IOException e){
System.out.println(e);
}
}
}
输出结果为：Welcome to read my blog！ //此处内容与写入内容一致。
文件字节流的应用：存在一个已知文件oldfile，用文件字节流进行复制到新的文件newfile，并输出newfile中的内容
public void CopyFile(String oldFilename,String newFilename){
File nfile = new File(newFilename);
File ofile = new File(oldFilename);
FileOutputStream out = null;
FileInputStream in = null;
String str = new String();
try{
in = new FileInputStream(ofile);
int a = in.read();
while(a != -1){
str += (char)a;
a = in.read();
}
}catch(IOException e){
System.out.println(e);
}
byte b[] = str.getBytes();
try{
out = new FileOutputStream(nfile);
out.write(b);
out.flush();
out.close();
}catch(IOException e){
System.out.println(e);
}
}
@Test
public void test2() throws IOException{
File oldfile = new File("hello.txt");
File newfile = new File("hel.txt");
FileInputStream in = null;
CopyFile(oldfile.getName(),newfile.getName());
try{
in = new FileInputStream(newfile);
int a = in.read();
String str = new String();
while(a != -1){
str += (char)a;
a = in.read();
}
System.out.println(str);
}catch(IOException e){
System.out.println(e);
}
}
输出结果为：文件 oldfile 中的内容。