Search code examples
java-9jshell

How to take user input in jshell script?

Question:

How to take user input in jshell script? or what I'm doing wrong?

Note: I'm NOT looking how to pass arguments to jshell script.

Example:

For example script hello.java:

Scanner in = new Scanner(System.in);

System.out.print("Enter number n1: ");
int n1 = in.nextInt();
System.out.print("Enter number n2: ");
int n2 = in.nextInt();

System.out.println("n1 + n2 = "+ (n1 +n2));

/exit

It works if I type line by line in jshell, but then I run jshell hello.java it doesn't. Throws java.util.NoSuchElementException.

Output I getting:

@myMint ~/Java $ jshell hello.java 
Enter number n1: |  java.util.NoSuchElementException thrown: 
|        at Scanner.throwFor (Scanner.java:858)
|        at Scanner.next (Scanner.java:1497)
|        at Scanner.nextInt (Scanner.java:2161)
|        at Scanner.nextInt (Scanner.java:2115)
|        at (#3:1)
Enter number n2: |  java.util.NoSuchElementException thrown: 
|        at Scanner.throwFor (Scanner.java:858)
|        at Scanner.next (Scanner.java:1497)
|        at Scanner.nextInt (Scanner.java:2161)
|        at Scanner.nextInt (Scanner.java:2115)
|        at (#5:1)
n1 + n2 = 0

My system: Linux Mint 18.2(x64), JShell Version 9.0.1

Solution

  • Per default, jshell delegates execution to a remote VM. If you pass --execution local it uses the same VM process, which provides an instance of System.in as expected. Tailored to your question, the following call should do the trick:

    jshell --execution local hello.java

    See details via jshell --help-extra or browse the API documentation at https://docs.oracle.com/en/java/javase/11/docs/api/jdk.jshell/module-summary.html