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.



Sar Maroof is a professional software development teacher, gives master classes and publishes technical articles. He is also an expert software developer and worked for several big as well as small companies and later as a freelancer.
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  1. Your articles are for when it abeulotsly, positively, needs to be understood overnight.

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