下面两个不同的代码为我提供了Java中的两个不同的输出

Question

See the below two code and let me know why it is printing like that this is java language

BufferedReader br = new BufferedReader(new FileReader("file path"));
while(br.readLine()!= null) {
    System.out.println(br.readLine());
}
br.close();

This code doesn't print complete file content, however if i use below code it prints complete content of file..please explain

BufferedReader br = new BufferedReader(new FileReader("filepath"));
String str;
while((str=br.readLine())!= null) {
    System.out.println(str);
}
br.close();

Answer 1

Simple: you read lines twice from the BufferedReader , by calling br.readLine() twice in your while loop. First a line is read in the condition part ( while (br.readLine()!=null) ) and later again to print it ( ...println(br.readLine()) ).

A line that is read is gone from the buffer.

In your second code part, the line is stored to str in the condition part. That str is later also used to print the line.

Answer 2

您在第一次在while条件中使用br.readLine()并在System.out.println(br.readLine())中第二次使用br.readLine()读取了两次，这就是为什么它总是打印2,4,6,8...行和在第二个代码中，您只需读取一次，并将其存储在str变量中并打印str ，这就是为什么要打印整个文件的原因。