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.

Articles: ArrayList  HashSet  TreeSet  HashMap  TreeMap 
Quizzes: Java Collection Quizzes 

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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.


Articles: ArrayList  HashSet  TreeSet  HashMap  TreeMap 
Quizzes: Java Collection Quizzes 
Please, leave your questions, feedback and suggestions in the comments below!
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Sar Maroof is the author of two Java books namely, Java quizmaster for beginners and A guide to build a Java application.
Experience with developing web applications since 2001
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Applied Science in Physics HBO Amsterdam
As well as Bachellor Science in Physics.
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  1. Your articles are for when it abeulotsly, positively, needs to be understood overnight.

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