Push Operation on Stack in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to push an element onto the stack.

DSA Java

stack.[1](value);

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

Aremove

Bpop

Cpeek

Dpush

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() instead of push() removes an element instead of adding.

Using peek() only views the top element without adding.

The push() method adds an element to the top of the stack.

2fill in blank

medium

Complete the code to check if the stack is empty before pushing.

DSA Java

if (stack.[1]()) {
    stack.push(value);
}

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

AisFull

BisEmpty

Csize

Dcontains

Attempts:

3 left

💡 Hint

Common Mistakes

Using isFull() checks if stack is full, not empty.

Using size() returns the number of elements but does not return boolean.

The isEmpty() method checks if the stack has no elements.

3fill in blank

hard

Fix the error in the push method call to add element 10.

DSA Java

stack.[1](10);

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

Apop

Bpeek

Cpush

Dpoll

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() removes the top element instead of adding.

Using peek() only views the top element.

push(10) correctly adds the element 10 to the stack.

4fill in blank

hard

Fill both blanks to push value 5 onto the stack only if it is not full.

DSA Java

if (!stack.[1]()) {
    stack.[2](5);
}

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

AisFull

Bpush

Cpop

DisEmpty

Attempts:

3 left

💡 Hint

Common Mistakes

Using isEmpty() instead of isFull() to check capacity.

Using pop() instead of push() to add element.

Check if stack is not full with isFull(), then push the value.

5fill in blank

hard

Fill all three blanks to push the uppercase version of a string onto the stack if it is not empty.

DSA Java

if (!stack.[1]()) {
    stack.[2](word.[3]());
}

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

AisEmpty

Bpush

CtoUpperCase

Dpop

Attempts:

3 left

💡 Hint

Common Mistakes

Using pop() instead of push() to add element.

Using toLowerCase() instead of toUpperCase() for conversion.

Check stack is not empty with isEmpty(), then push the uppercase word using toUpperCase().

Practice

1. What does the push operation do in a stack?

easy

A. Adds an element to the top of the stack

B. Removes the top element from the stack

C. Checks if the stack is empty

D. Returns the bottom element of the stack

Solution

1. Step 1: Understand stack behavior

   A stack follows Last In First Out (LIFO) principle, so new elements are added on top.

2. Step 2: Define push operation

   The push operation adds a new element to the top of the stack, increasing its size by one.

3. Final Answer:

   Adds an element to the top of the stack -> Option A

4. Quick Check:

   Push = Add top element [OK]

Hint: Push always adds element on top of stack [OK]

Common Mistakes:

• Confusing push with pop
• Thinking push removes element
• Assuming push adds at bottom

2. Which of the following is the correct syntax to push an integer 10 onto a stack named stack in Java?

easy

A. stack.add(10);

B. stack.push(10);

C. stack.insert(10);

D. stack.put(10);

Solution

1. Step 1: Recall Java Stack API

   Java's Stack class uses the method push() to add elements.

2. Step 2: Match correct method

   Among options, only push() is the correct method to add elements to a stack.

3. Final Answer:

   stack.push(10); -> Option B

4. Quick Check:

   Java stack push method = push() [OK]

Hint: Use push() method to add elements in Java stack [OK]

Common Mistakes:

• Using add() which is for lists
• Using insert() which doesn't exist
• Using put() which is for maps

3. What will be the output after executing the following Java code?

Stack<Integer> stack = new Stack<>();
stack.push(5);
stack.push(10);
stack.push(15);
System.out.println(stack);

medium

A. [5, 15, 10]

B. [15, 10, 5]

C. [10, 15, 5]

D. [5, 10, 15]

Solution

1. Step 1: Trace push operations

   Elements 5, 10, and 15 are pushed in order, so stack stores them as [5, 10, 15].

2. Step 2: Understand Stack's toString()

   Java's Stack prints elements from bottom to top in list format, so output is [5, 10, 15].

3. Final Answer:

   [5, 10, 15] -> Option D

4. Quick Check:

   Stack print shows bottom to top [OK]

Hint: Stack prints bottom to top in Java [OK]

Common Mistakes:

• Assuming print shows top element first
• Confusing stack with queue order
• Expecting reversed list output

4. Identify the error in the following code snippet that tries to push an element onto a stack:

Stack<String> stack = new Stack<>();
stack.push("Hello");
stack.push(100);

medium

A. Stack must be initialized with size

B. Stack class does not have push method

C. Cannot push integer 100 into a Stack of Strings

D. Missing semicolon after push statements

Solution

1. Step 1: Check stack type and pushed elements

   The stack is declared to hold Strings only, but 100 is an integer.

2. Step 2: Identify type mismatch error

   Pushing an integer into a String stack causes a compile-time type error.

3. Final Answer:

   Cannot push integer 100 into a Stack of Strings -> Option C

4. Quick Check:

   Type mismatch error = pushing wrong data type [OK]

Hint: Stack type must match pushed element type [OK]

Common Mistakes:

• Ignoring generic type mismatch
• Thinking push method missing
• Assuming size needed at init

5. Given an empty stack, which sequence of push operations will result in the stack containing elements in this order from bottom to top: 3 -> 7 -> 5 -> null?

hard

A. push(3), push(7), push(5)

B. push(5), push(7), push(3)

C. push(7), push(3), push(5)

D. push(5), push(3), push(7)

Solution

1. Step 1: Understand stack order after pushes

   Elements pushed first are at bottom, last pushed at top.

2. Step 2: Match push order to desired stack

   To get 3 at bottom, then 7, then 5 on top, push in order: 3, then 7, then 5.

3. Final Answer:

   push(3), push(7), push(5) -> Option A

4. Quick Check:

   Push order = bottom to top [OK]

Hint: Push elements in bottom-to-top order [OK]

Common Mistakes:

• Reversing push order
• Confusing push with pop order
• Assuming stack inserts at bottom