Quizzes – Java collections

The following Java exercise(s) are designed to help you understand the article to which it belongs. If the following quizzes are too hard, then I recommend to read the article first, which offers a theoretical explanation including examples and exercises.

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Quiz 1: Learn more about Java ArrayLists

What is written to the standard output as the result of executing the following code?

import java.util.ArrayList;

public class MyClass {

	public static void main(String[] args){
		ArrayList<String> prLanguage = new ArrayList<String>();
		prLanguage.add("Java");
		prLanguage.add("C++");
		prLanguage.add("Python");
		prLanguage.add("PHP");
		prLanguage.add("Ruby");
		prLanguage.add("Perl");

		prLanguage.add(3,null);
		prLanguage.add(3,null);
		prLanguage.add(4,"PHP");

		for(int i = 0; i &lt; prLanguage.size(); i ++ ) {
			System.out.print(" " + prLanguage.get(i));
		}
	}
}

Select the correct answer.


 

Quiz 2: How the elements of a TreeMap behave?

What is written to the standard output as the result of executing the following code?

import java.util.Iterator;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

public class MyClass {

	public static void main(String[] args){

		TreeMap countryMap = new TreeMap();
		countryMap.put("US","United States");
		countryMap.put("CN","China");
		countryMap.put("RU","Russia");
		countryMap.put("FR","France");
		countryMap.put("FR","France");
		countryMap.put("DE","Germany");
		countryMap.put("AU","Australia");
		countryMap.put("Au","Australia");
		countryMap.put("NU",null);

		Set set = countryMap.entrySet();
		Iterator iter = set.iterator();
		while(iter.hasNext()) {
			Map.Entry entry = (Map.Entry) iter.next();
			System.out.print(" " + entry.getValue());
		}
	}
}

Select the correct answer.


 

Quiz 3: An easy example using a HashSet

What is written to the standard output as the result of executing the following code?

import java.util.HashSet;
import java.util.Iterator;

public class MyClass {

	public static void main(String[] args){

		HashSet<String> citySet = new HashSet<String>();
		citySet.add(" Shanghai,");
		citySet.add(" Delhi,");
		citySet.add(" " + null + ",");
		citySet.add(" Moscow,");
		citySet.add(" London,");
		citySet.add(" New York,");
		citySet.add(" London,");

		Iterator<String> iter = citySet.iterator();
		while(iter.hasNext()) {
			System.out.print(" " + iter.next());
		}
	}
}

Select the correct answer.


Please, leave your questions, feedback and suggestions in the comments below!
SarMaroof.com offers a practical method to learn and improve your Java skills. It avoids unnecessary long boring theoretical explanations, but it uses many exercises and quizzes.


Sar Maroof is graduated from HBO Amsterdam “higher professional education” when he already had a bachelor of science degree in Physics.
He is a SUN certified JSP as well as EJB. He has experience with Java since 2001 and worked for several big as well as small companies and later as a freelancer.
He is the author of Java quizmaster and Build a Java application in 7 days.

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  1. Your articles are for when it abeulotsly, positively, needs to be understood overnight.

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