Java Scanner does not wait for input

Question

I have two blocks of code here. One scanner properly waits user input, and the other just blows right through it and calls `nextInt()` which returns a `NoSuchElementException`. Here is the block that works: ``` public void startGame() { out.println("Player1: 1 for dumb player, 2 for smart player, 3 for human player."); Scanner scan = new Scanner(System.in); p = scan.nextInt(); if (p == 1) p1 = new DumbPlayer("ONE"); if (p == 2) p1 = new SmartPlayer("ONE"); else p1 = new HumanPlayer("ONE"); out.println("Player2: 1 for dumb player, 2 for smart player, 3 for human player."); p = scan.nextInt(); if (p == 1) p2 = new DumbPlayer("TWO"); if (p == 2) p2 = new SmartPlayer("TWO"); else p2 = new HumanPlayer("TWO"); scan.close(); ``` And here is the block that does not: ``` public int findBestMove(Set moves, Board b) { Set set = new HashSet(); out.println("Player " +name+ ", select a column from 1-7: "); Scanner scan = new Scanner(System.in); <--here it should wait for…

Accepted Answer

According to the java.util.Scanner javadoc, `Scanner.close()` closes the associated stream if this stream implements the `Closeable` interface. `java.lang.System.in` is an InputStream, which implements the `Closeable` interface. Hence, after calling `Scanner.close()` on a `Scanner` which is associated with `System.in`, the `System.in` stream is closed and not available anymore.

The following SSCCE works for me. I have removed some code from the question which is not relevant to the actual issue. Note that with this approach, while it works, Eclipse gives me the warning `"Resource leak: 'scan' is never closed"`, so a better solution would be to use one Scanner instance only.

```
package com.example;

import java.util.Scanner;
import java.util.Set;
import static java.lang.System.out;

public class ScannerTest {
    int p = 0;
    String name = "Test";

public void startGame() {
        out.println("Player1: 1 for dumb player, 2 for smart player, 3 for human player.");
        Scanner scan = new Scanner(System.in);
        p = scan.nextInt();

out.println("Result1: " + p);

out.println("Player2: 1 for dumb player, 2 for smart player, 3 for human player.");
        p = scan.nextInt();

out.println("Result2: " + p);

// scan.close();   // Do not close the Scanner to leave System.in open
    }

public int findBestMove(Set<Integer> moves, Object /*Board*/ b) {
        out.println("Player " +name+ ", select a column from 1-7: ");
        Scanner scan = new Scanner(System.in);
        int move = scan.nextInt();
        // scan.close();   // Do not close the Scanner to leave System.in open

out.println("Move: " + move);

return 0;
    }

public void run() {
        startGame();
        findBestMove(null, null);
    }

public static void main(String[] args) {
        ScannerTest st = new ScannerTest();
        st.run();
    }
}
```

Java Scanner does not wait for input

Solution

Problem

Related problems