5 Java Programming Test Questions for Interview

Recently I am taking a lot of interview for my organization. So I was in the search of some java programming test questions that are little bit tricky also. Here I am providing five of the tricky questions I found interesting and need a closer look to understand. The explanation will be provided after the questions. Test your knowledge of java by trying to provide the answer of the below test questions. Java Programming Test Question 1
What is the output of the below statements?

String s1 = "abc";

String s2 = "abc";

System.out.println("s1 == s2 is:" + s1 == s2);

The given statements output will be “false” because in java + operator precedence is more than == operator. So the given expression will be evaluated to “s1 == s2 is:abc” == “abc” i.e false.
What is the output of the below statements?

HashSet shortSet = new HashSet();

for (short i = 0; i < 100; i++) {

    shortSet.add(i);

    shortSet.remove(i - 1);

}

System.out.println(shortSet.size());

The size of the shortSet will be 100. Java Autoboxing feature has been introduced in JDK 5, so while adding the short to HashSet<Short> it will automatically convert it to Short object. Now “i-1″ will be converted to int while evaluation and after that it will autoboxed to Integer object but there are no Integer object in the HashSet, so it will not remove anything from the HashSet and finally its size will be 100.

String s3 = "JournalDev";
int start = 1;
char end = 5;
System.out.println(start + end);
System.out.println(s3.substring(start, end));

1. The given statements output will be "ourn". First character will be automatically type caste to int. After that since in java first character index is 0, so it will start from 'o' and print till 'n'. Note that in String substring function it leaves the end index.

try {
 if (flag) {
  while (true) {
  }
 } else {
  System.exit(1);
 }
} finally {
 System.out.println("In Finally");
}

1. The finally block will never be reached here. If flag will be TRUE, it will go into an infinite loop and if its false its exiting the JVM. So finally block will never be reached here.

1. String str = null;
   String str1="abc";
   System.out.println(str1.equals("abc") | str.equals(null));

1. The given print statement will throw java.lang.NullPointerException because while evaluating the OR logical operator it will first evaluate both the literals and since str is null, .equals() method will throw exception. Its always advisable to use short circuit logical operators i.e "||" and "&&" which evaluates the literals values from left and since the first literal will return true, it will skip the second literal evaluation.

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