Reference data types in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a String variable named greeting.

Java

String greeting = [1];

Drag options to blanks, or click blank then click option'

A"Hello"

BHello

Cchar[]

Dint

Attempts:

3 left

💡 Hint

Common Mistakes

Forgetting the quotes around the text.

Using single quotes instead of double quotes.

In Java, String values must be enclosed in double quotes.

2fill in blank

medium

Complete the code to create a new Integer object with value 10.

Java

Integer number = [1];

Drag options to blanks, or click blank then click option'

Anew Integer(10)

BInteger(10)

C10

Dint(10)

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to call the constructor without new.

Assigning a primitive int directly to an Integer without autoboxing.

To create an Integer object, use the new keyword with the constructor.

3fill in blank

hard

Fix the error in the code to compare two String objects correctly.

Java

if (str1.[1](str2)) {
    System.out.println("Strings are equal");
}

Drag options to blanks, or click blank then click option'

A==

Bequals

Cequals()

DcompareTo()

Attempts:

3 left

💡 Hint

Common Mistakes

Using == to compare Strings, which compares references, not content.

Using equals without parentheses, which is a syntax error.

Use the equals() method to compare the contents of two String objects.

4fill in blank

hard

Fill both blanks to create an array of Strings and assign a value to the first element.

Java

String[] names = new String[[1]];
names[[2]] = "Alice";

Drag options to blanks, or click blank then click option'

A3

B0

C1

Dnew String[3]

Attempts:

3 left

💡 Hint

Common Mistakes

Using 1 as the first index instead of 0.

Confusing the array size with the index.

The array size is 3, and the first element index is 0.

5fill in blank

hard

Fill all three blanks to create a HashMap, add a key-value pair, and retrieve a value.

Java

Map<String, Integer> map = new [1]<>();
map.[2]("age", 25);
int age = map.[3]("age");

Drag options to blanks, or click blank then click option'

AHashMap

Bput

Cget

DTreeMap

Attempts:

3 left

💡 Hint

Common Mistakes

Using TreeMap instead of HashMap (both work but only one is correct here).

Using get to add entries or put to retrieve values.

Use HashMap to create the map, put to add entries, and get to retrieve values.