Use java.io.tmpdir to get system tmp directory.

TmpDirExample.java

import java.io.File;
import java.io.IOException;


public class TmpDirExample {
    public static void main(String[] args) {
        String tmpdir = System.getProperty("java.io.tmpdir");
        System.out.println("The default value of the java.io.tmpdir system property is: \""
                + tmpdir  + "\"\n");

        //Specify some temporary files.
        String prefix = "file";
        String suffix = ".txt";
        
        File tempFile = null;
        File tempFile2 = null;
        File tempFile3 = null;
        File directory = new File("/home/stathis");
        
        try {
            //Create two temporary files.
            tempFile = File.createTempFile(prefix, suffix);
            tempFile2 = File.createTempFile(prefix, null);
            tempFile3 = File.createTempFile(prefix, suffix, directory);
        }
        catch (IOException ex) {
            System.err.println("An IOException was caught: " + ex.getMessage());
            ex.printStackTrace();
        }

        //Printing the name of every file.
        System.out.println("A new file called \"" + tempFile.getName()
                + "\" was created in the directory: \"" + tmpdir + "\"");
        
        System.out.println("A new file called \"" + tempFile2.getName()
                + "\" was created in the directory: \"" + tmpdir + "\"\n");
        
        System.out.println("A new file called \"" + tempFile3.getName()
                + "\" was created in the directory: \"" + directory.getName() + "\"\n");
        
        //Printing the parent directories of every file.
        System.out.println("The parent directory of the file \"" + tempFile.getName()
                + "\" is: \"" + tempFile.getParent() + "\"");
        System.out.println("The parent directory of the file \"" + tempFile2.getName()
                + "\" is: \"" + tempFile2.getParent() + "\"");
        System.out.println("The parent directory of the file \"" + tempFile3.getName()
                + "\" is: \"" + tempFile3.getParent() + "\"\n");
        
        //Delete the temporary files.
        if(tempFile.delete())
            System.out.println("Successfully deleted the file with name: \""
                + tempFile.getName() + "\"");
        else
            System.out.println("Couldn't delete the file with name: \"" + tmpdir + "\"");
        
        if(tempFile2.delete())
            System.out.println("Successfully deleted the file with name: \""
                + tempFile2.getName() + "\"");
        else
            System.out.println("Couldn't delete the file with name: \"" + tmpdir + "\"");
        
        if(tempFile3.delete())
            System.out.println("Successfully deleted the file with name: \""
                + tempFile3.getName() + "\"");
        else
            System.out.println("Couldn't delete the file with name: \"" + tmpdir + "\"");
    }
}