Read standard input in Java

This article is based on the motivation of other powers, "I don't know the best practices, so if you write them in Qiita for the time being, a detailed person will tell you" rather than "showing the best practices yourself". Masu (´ ・ ω ・ `) A test that tries to follow the collective intelligence of the Internet.

First of all, the one that uses BufferedReader is often found in blog articles on the Internet.

var stdin = new BufferedReader(new InputStreamReader(;

//Read standard input line by line.
String line;
while ((line = stdin.readLine()) != null) {

//If the value given from the standard input is a numerical value, you need to convert it yourself.
while ((line = stdin.readLine()) != null) {
    int i = Integer.valueOf(line);

//Easy to connect to stream.

To briefly summarize the advantages and disadvantages of this method,

--Easy to find samples on the net. This "rich sample" is not surprising in practical programming. ――However, compared to the Scanner described later, there are more types, and script-level programming is a little troublesome. ――It's hard to say that it's beautiful even if you understand it when you write the constructor twice (´ ・ ω ・ `) --Easy to connect to Stream introduced from Java8. --Since it is buffered, it seems to work at high speed (unconfirmed) --You need to handle the checked exception IOException. This is a bit annoying at a little script level.

By the way, personally speaking, 90% of competitive programming uses standard input in Java. In short, there are many cases where you want to write a little and move it a little. In addition, it is common in competitive programming to use an input format such as "the first line is a numerical value, and the second and subsequent lines are character strings". In such cases, it is necessary to quickly handle various types of input. I think that Scanner is often more convenient in such cases.

var stdin = new Scanner(;

//Read standard input line by line.
while (stdin.hasNextLine()) {
    var line = stdin.nextLine();

//For example, if you have the following input---> 1000 10.005 HOGE
//Even such a complicated input is relatively easy to process.
int i = stdin.nextInt();
double d = stdin.nextDouble();
String s = stdin.nextLine();

//It's a little difficult to connect to Stream. In order to use mapToObj etc., some ingenuity is required.

Here too, I will summarize the advantages and disadvantages.

--Anyway, it's multifunctional. Easy to handle complex inputs. ――I can't help but think, "I don't understand because it's too multifunctional." Aside from competitive programming, I wonder if there is such a complicated input in practice. ――Since it does not throw inspection exceptions, it is convenient when you want to write a little and move it a little. --It's hard to connect to Stream. It's hard to use Function anyway. --Whether it is buffered depends on the implementation. Probably not (unconfirmed)

Writing this way, both seem to have advantages and disadvantages (naturally). The latter is easier for a bit of script-level programming, but the former is definitely more modern. It seems good to adopt the former in practical programming (´ ・ ω ・ `)

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