Import statement usage in Java - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to import the ArrayList class from java.util package.

Java

import java.util.[1];

public class Main {
    public static void main(String[] args) {
        ArrayList<String> list = new ArrayList<>();
    }
}

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

AArrayList

BScanner

CHashMap

DLinkedList

Attempts:

3 left

💡 Hint

Common Mistakes

Importing the wrong class like Scanner or HashMap.

Forgetting to import the class.

The ArrayList class is in the java.util package, so you import it with import java.util.ArrayList;.

2fill in blank

medium

Complete the code to import all classes from the java.io package.

Java

import java.io[1];

public class Main {
    public static void main(String[] args) {
        // code using java.io classes
    }
}

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

A.all

B.*

C.allClasses

D.allFiles

Attempts:

3 left

💡 Hint

Common Mistakes

Using incorrect wildcard like '.all' or '.allClasses'.

Forgetting the dot before the asterisk.

To import all classes from a package, use .* after the package name, like import java.io.*;.

3fill in blank

hard

Fix the error in the import statement to correctly import the HashMap class.

Java

import java.util.[1];

public class Main {
    public static void main(String[] args) {
        HashMap<String, Integer> map = new HashMap<>();
    }
}

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

AHashMap

Bhashmap

CHashmap

DhashMap

Attempts:

3 left

💡 Hint

Common Mistakes

Using lowercase 'm' in HashMap.

Misspelling the class name.

Java is case-sensitive. The correct class name is HashMap with capital M.

4fill in blank

hard

Fill both blanks to import the Scanner class and create a Scanner object.

Java

import java.util.[1];

public class Main {
    public static void main(String[] args) {
        [2] scanner = new Scanner(System.in);
    }
}

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

AScanner

CArrayList

DHashMap

Attempts:

3 left

💡 Hint

Common Mistakes

Importing the wrong class.

Using a different type name than the imported class.

You import the Scanner class and declare a variable of type Scanner to create the object.

5fill in blank

hard

Fill all three blanks to import the List interface, declare a List variable, and initialize it with an ArrayList.

Java

import java.util.[1];
import java.util.[2];

public class Main {
    public static void main(String[] args) {
        [3]<String> list = new ArrayList<>();
    }
}

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

AList

BArrayList

Attempts:

3 left

💡 Hint

Common Mistakes

Not importing both classes.

Using ArrayList as the variable type instead of List.

You import both List and ArrayList classes. Then declare a variable of type List and initialize it with an ArrayList object.

Practice

1. What is the main purpose of an import statement in Java?

easy

A. To allow the use of classes from other packages without full package names

B. To declare a new package for the current class

C. To create a new class in the program

D. To start the main method of the program

Solution

1. Step 1: Understand the role of import statements

   Import statements let you use classes from other packages without writing their full package names every time.

2. Step 2: Differentiate from other Java keywords

   Import does not declare packages, create classes, or start methods; it only helps with class usage.

3. Final Answer:

   To allow the use of classes from other packages without full package names -> Option A

4. Quick Check:

   Import = Use classes easily [OK]

Hint: Import lets you use classes without full package names [OK]

Common Mistakes:

• Confusing import with package declaration
• Thinking import creates classes
• Assuming import runs code

2. Which of the following is the correct syntax to import all classes from the package java.util?

easy

A. import java.util.all;

B. import java.util;

C. import * from java.util;

D. import java.util.*;

Solution

1. Step 1: Recall the syntax for importing all classes

   To import all classes from a package, use the asterisk (*) after the package name with a semicolon.

2. Step 2: Check each option's syntax

   Only import java.util.*; is correct. Others miss the asterisk or use wrong keywords.

3. Final Answer:

   import java.util.*; -> Option D

4. Quick Check:

   Use * to import all classes [OK]

Hint: Use * after package name to import all classes [OK]

Common Mistakes:

• Omitting the asterisk (*) when importing all classes
• Missing semicolon at the end
• Using incorrect keywords like 'all' or 'from'

3. What will be the output of the following code?

import java.util.ArrayList;
public class Test {
  public static void main(String[] args) {
    ArrayList<String> list = new ArrayList<>();
    list.add("Hello");
    list.add("World");
    System.out.println(list.get(1));
  }
}

medium

A. ArrayList

B. Hello

C. World

D. Compilation error

Solution

1. Step 1: Understand the import and list usage

   The code imports ArrayList correctly and creates a list with "Hello" at index 0 and "World" at index 1.

2. Step 2: Check the printed element

   list.get(1) accesses the second element, which is "World".

3. Final Answer:

   World -> Option C

4. Quick Check:

   list.get(1) = World [OK]

Hint: Index 1 means second element in list [OK]

Common Mistakes:

• Confusing index 0 and 1
• Assuming import causes error
• Thinking output is class name

4. Identify the error in the following code snippet:

import java.util.List;
public class Demo {
  public static void main(String[] args) {
    List<String> items = new ArrayList<>();
  }
}

medium

A. Missing semicolon after import statement

B. ArrayList is not imported

C. List cannot be used without initialization

D. No error, code is correct

Solution

1. Step 1: Check import statements

   The code imports List but does not import ArrayList, which is used in the code.

2. Step 2: Identify missing import causing error

   ArrayList must be imported from java.util to be used; missing import causes compilation error.

3. Final Answer:

   ArrayList is not imported -> Option B

4. Quick Check:

   Missing import for ArrayList causes error [OK]

Hint: Import all classes you use explicitly [OK]

Common Mistakes:

• Forgetting semicolon after import
• Assuming List needs initialization differently
• Ignoring missing imports for used classes

5. You want to use both java.util.Date and java.sql.Date in the same Java file. How should you import them to avoid confusion?

hard

A. import java.util.Date;
// Use fully qualified name for java.sql.Date in code

B. import java.util.*;
import java.sql.*;

C. import java.util.Date;
import java.sql.Date;

D. import java.util.*;
import java.sql.Date;

Solution

1. Step 1: Understand class name conflict

   Both packages have a class named Date, so importing both directly causes ambiguity.

2. Step 2: Use import for one and full name for the other

   Import one Date class and use the full package name for the other to avoid confusion.

3. Final Answer:

   import java.util.Date; // Use fully qualified name for java.sql.Date in code -> Option A

4. Quick Check:

   Import one Date, fully qualify the other [OK]

Hint: Import one class, fully qualify the other to avoid name clash [OK]

Common Mistakes:

• Importing both classes directly causing ambiguity
• Using wildcard imports causing confusion
• Not using fully qualified names when needed