Java读取文件-BufferedReader/FileReader/InputStreamReader/FileInputStream的关系和区别

InputStreamReader inputstreamreader1=new InputStreamReader(System.in);
InputStreamReader inputstreamreader2=new InputStreamReader(new FileInputStream("/opt/xxx"));
InputStreamReader inputstreamreader3=new InputStreamReader(new FileInputStream(new File("/opt/xxx")));

FileReader f1=new FileReader("/opt/xxx.txt");
FileReader f2=new FileReader(new File("/opt/xxx.txt"));

BufferedReader buffered_filereader=new BufferedReader(new FileReader(filename));
BufferedReader buffered_inputstreamreader=new BufferedReader(new InputStreamReader(fileinputstream));

String read;
while((read=buffered_filereader.readLine())!=null){
    System.out.println(read);
}

int i;
while ((i=filereader.read())!=-1){
    System.out.print((char)i);
}

String filename="/opt/xxx.log";
 
FileInputStream fileinputstream=new FileInputStream(filename);
InputStreamReader inputstreamreader=new InputStreamReader(fileinputstream);
int i;
while ((i=inputstreamreader.read())!=-1){
    System.out.print((char)i);
}

String filename="/opt/xxx.log";
 
FileReader filereader=new FileReader(filename);
int i;
while ((i=filereader.read())!=-1){
    System.out.print((char)i);
}

String filename="/opt/xxx.log";
 
FileReader filereader=new FileReader(filename);
BufferedReader buffered_filereader=new BufferedReader(filereader);
String read;
while((read=buffered_filereader.readLine())!=null){
    System.out.println(read);
}

String filename="/opt/xxx.log";
FileInputStream fileinputstream=new FileInputStream(filename);
InputStreamReader inputstreamreader=new InputStreamReader(fileinputstream);
BufferedReader buffered_inputstreamreader=new BufferedReader(inputstreamreader);
String read;
while((read=buffered_inputstreamreader.readLine())!=null){
    System.out.println(read);
}