Using Random to generate random numbers in Android

MainActivity is as follows:

package cc.test;

import java.util.HashSet;
import java.util.Random;
import android.app.Activity;
import android.os.Bundle;
/**
 *
 * Demo description:
 * Use Random to generate random numbers in Java
 *
 * References:
 * 1 http://blog.csdn.net/herrapfel/article/details/1885016
 * 2 http://blog.csdn.net/yuxuepiaoguo/article/details/4195198
 * 3 http://blog.csdn.net/zhongyili_sohu/article/details/7906125
 * 4 http://www.csdn.net/article/2012-03-22/313407
 *   Thank you very much
 */
public class TestRandomActivity extends Activity {
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate (savedInstanceState);
        setContentView(R.layout.main);
        testRandom1();
        testRandom2();
        testRandom3();
    }
    
    
    
    //generate random numbers
    private void testRandom1(){
    	Random random=new Random();
    	for (int i = 0; i <5; i++) {
			System.out.println("random.nextInt()="+random.nextInt());
		}
    	System.out.println("/////The above is the test of testRandom1()///////");
    }
    
    
    
    //Generate random numbers within a certain range.
    //For example, here it is required to generate random numbers within [0 - n).
    //Note: include 0 but not n
    private void testRandom2(){
    	Random random=new Random();
    	for (int i = 0; i <10; i++) {
			System.out.println("random.nextInt()="+random.nextInt(20));
		}
    	System.out.println("/////The above is the test of testRandom2()///////");
    }
    
    
    //Generate non-repeating random numbers within a certain range
    // The random numbers generated in testRandom2 may be duplicated.
    // avoid the problem here
    private void testRandom3(){
    	HashSet integerHashSet=new HashSet();
    	Random random=new Random();
    	for (int i = 0; i <10; i++) {
    		int randomInt=random.nextInt(20);
    		System.out.println("Generated randomInt="+randomInt);
    		if (!integerHashSet.contains(randomInt)) {
    			integerHashSet.add(randomInt);
    			System.out.println("randomInt="+randomInt added to HashSet);
			}else {
				System.out.println("The number has been added and cannot be added repeatedly");
			}
		}
    	System.out.println("/////The above is the test of testRandom3()///////");
    }
    
}