CODEWITHSUNDEEP
javafilerandom
Kevin Hernandez
Kevin Hernandez

Reputation: 1400

Pick a random file from a directory in Java

I would like to pick a random file from any directory I want. such as C:\Users\Josh\Pictures\[randomFile]

I have no code to show I just would like to know how I would come by doing that.

What I am fully doing is using a class to change the background of my desktop, and now I want to add a random file to it so when it refreshes the background will be different and I wont have to stop the running code to manually change the name of the file in the path. If you are wondering heres what it looks like 

import java.io.File;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;


public class BackgroundTest {

    final static File dir = new File("C:\\Users\\Kevin\\Pictures\\Pyimgur\\");
    static int size = 10;
    static String [] fileArray = new String[size];





public static void main(String[] args) {
    File[] files = dir.listFiles();
    for(int i =0; i<size;i++){
        int idz = (int)(Math.random()*size);
        fileArray[i]=files[idz].getName();

    }

    for(String x: fileArray){
        System.out.print(x);
    }

    String path = "C:\\Users\\Kevin\\Pictures\\Pyimgur\\";
    String picture = "picture.jpg";
    //System.out.print(fileArray[0]);

    SPI.INSTANCE.SystemParametersInfo(
            new UINT_PTR(SPI.SPI_SETDESKWALLPAPER),
            new UINT_PTR(0),
            path + picture,
            new UINT_PTR(SPI.SPIF_UPDATEINIFILE | SPI.SPIF_SENDWININICHANGE));
}

public interface SPI extends StdCallLibrary {

    //from MSDN article
    long SPI_SETDESKWALLPAPER = 20;
    long SPIF_UPDATEINIFILE = 0x01;
    long SPIF_SENDWININICHANGE = 0x02;

    SPI INSTANCE = (SPI) Native.loadLibrary("user32", SPI.class, new HashMap<Object, Object>() {
        {
            put(OPTION_TYPE_MAPPER, W32APITypeMapper.UNICODE);
            put(OPTION_FUNCTION_MAPPER, W32APIFunctionMapper.UNICODE);
        }
    });

    boolean SystemParametersInfo(
            UINT_PTR uiAction,
            UINT_PTR uiParam,
            String pvParam,
            UINT_PTR fWinIni
    );
    }
}

Upvotes: 2

Views: 11619

Answers (2)

passion
passion

Reputation: 1360

  1. Create an array of the files within the given directory using File.listFiles().
  2. Select a file based on a random index from this array.
    That can be done with an instance of the Random class, using Random.nextInt(int bound), where bound, in this case, is the amount of files in the array, thus the array's length.

Example:

File[] files = dir.listFiles();

Random rand = new Random();

File file = files[rand.nextInt(files.length)];

Upvotes: 13

CosmicGiant
CosmicGiant

Reputation: 6441

Scan the directory to make a list of the files in it, and then pick a random index from that list.

Then build upon that principle by filtering for valid files only (image files, in this case); avoiding the picking of the same image as the current one; and other such improvements...

Upvotes: 1

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