Array Insertion at End in DSA Java - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to insert an element at the end of the array.

DSA Java

int[] arr = new int[5];
int size = 0;
int element = 10;
arr[size[1]0] = element;
size++;

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

A/

B-

C*

D+

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' instead of '+' causes wrong index access.

Using '*' or '/' causes syntax or logic errors.

We use '+' to add the index offset. Here, size + 0 means the first empty position.

2fill in blank

medium

Complete the code to increase the size after insertion.

DSA Java

int[] arr = new int[5];
int size = 0;
arr[size] = 20;
size[1];

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

A-= 1

B*= 1

C+= 1

D/= 1

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-=' decreases size incorrectly.

Using '*=' or '/=' does not change size as intended.

We increase size by 1 after inserting an element to track the new end.

3fill in blank

hard

Fix the error in the insertion code to avoid ArrayIndexOutOfBoundsException.

DSA Java

int[] arr = new int[3];
int size = 3;
int element = 5;
if (size < arr.length) {
    arr[size[1]0] = element;
    size++;
}

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

A-

B+

C*

D/

Attempts:

3 left

💡 Hint

Common Mistakes

Using '-' causes negative index error.

Using '*' or '/' causes syntax errors.

Use '+' to insert at the current size index, which is the next free position.

4fill in blank

hard

Fill both blanks to complete the insertion and size update correctly.

DSA Java

int[] arr = new int[4];
int size = 2;
int element = 15;
if (size [1] arr.length) {
    arr[size[2]0] = element;
    size++;
}

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

A<

B>

C+

D-

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' causes wrong condition logic.

Using '-' causes wrong index calculation.

We check if size is less than array length and insert at size + 0 index.

5fill in blank

hard

Fill all three blanks to insert element and update size safely.

DSA Java

int[] arr = new int[5];
int size = 4;
int element = 25;
if (size [1] arr.length) {
    arr[size[2]0] = element;
    size[3];
}

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

A<

B+= 1

C+

D>

Attempts:

3 left

💡 Hint

Common Mistakes

Using '>' in condition causes logic error.

Using '-' for index causes wrong position.

Forgetting to increase size after insertion.

Check size < length, insert at size + 0, then increase size by 1.

Practice

1. What happens when you insert an element at the end of a fixed-size array in Java without resizing?

easy

A. The insertion throws an error if the array is full

B. The element is added at the next free position if available

C. The array automatically resizes to fit the new element

D. The element replaces the last element if the array is full

Solution

1. Step 1: Understand fixed-size array behavior

   Java arrays have a fixed size and cannot grow automatically. Attempting arr[size] where size == length throws ArrayIndexOutOfBoundsException.

2. Step 2: Inserting at end when full

   Standard insertion arr[size++] = element; if full (size == arr.length), accesses arr[length] and throws runtime error.

3. Final Answer:

   The insertion throws an error if the array is full -> Option A

4. Quick Check:

   Fixed-size array throws error when full [OK]

Hint: Fixed arrays don't resize; throws error if full [OK]

Common Mistakes:

• Assuming arrays resize automatically
• Thinking insertion overwrites last element
• Believing new element is added beyond array size

2. Which of the following is the correct syntax to insert an element at the end of an array in Java if the array has space?

easy

A. arr[size] = newElement; size++;

B. arr[arr.length - 1] = newElement;

C. arr[arr.length] = newElement;

D. arr.add(newElement);

Solution

1. Step 1: Understand array indexing and size tracking

   Arrays use zero-based indexing; last index is length-1. We track current size separately.

2. Step 2: Insert element at next free position

   Use size as index to insert, then increment size to reflect new element count.

3. Final Answer:

   arr[size] = newElement; size++; -> Option A

4. Quick Check:

   Use size as index and increment after insertion [OK]

Hint: Use size variable as index, then increment size [OK]

Common Mistakes:

• Using arr.length as index (out of bounds)
• Trying to use arr.add() which is for lists
• Overwriting last element without size tracking

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

int[] arr = new int[5];
int size = 0;
arr[size++] = 10;
arr[size++] = 20;
arr[size++] = 30;
System.out.print(java.util.Arrays.toString(arr));

medium

A. [10, 20, 30]

B. [10, 20, 30, 0, 0]

C. [10, 20, 30, 30, 30]

D. [0, 10, 20, 30, 0]

Solution

1. Step 1: Trace insertions with size increment

   Elements 10, 20, 30 are inserted at indexes 0, 1, 2 respectively; size increments after each insertion.

2. Step 2: Understand default array values

   Remaining positions (indexes 3 and 4) remain 0 as default for int arrays.

3. Final Answer:

   [10, 20, 30, 0, 0] -> Option B

4. Quick Check:

   Inserted elements at start; rest are zeros [OK]

Hint: Inserted elements fill start; rest remain default zero [OK]

Common Mistakes:

• Assuming array shrinks to inserted elements only
• Confusing index positions
• Expecting uninitialized elements to be null

4. Identify the error in the following code that tries to insert an element at the end of an array:

int[] arr = new int[3];
int size = 3;
arr[size] = 5;

medium

A. Compilation error due to wrong syntax

B. No error; element inserted at the end

C. ArrayIndexOutOfBoundsException because size equals array length

D. Logical error; element overwrites first element

Solution

1. Step 1: Check array size and index used

   Array length is 3, valid indexes are 0,1,2. Using index 3 causes error.

2. Step 2: Understand runtime exception

   Accessing arr[3] throws ArrayIndexOutOfBoundsException at runtime.

3. Final Answer:

   ArrayIndexOutOfBoundsException because size equals array length -> Option C

4. Quick Check:

   Index equals length causes runtime error [OK]

Hint: Index must be less than array length to avoid error [OK]

Common Mistakes:

• Assuming index == length is valid
• Expecting compile-time error instead of runtime
• Ignoring size variable correctness

5. You have an integer array of size 4: int[] arr = {1, 2, 3, 4}; and a variable size = 4;. You want to insert 5 at the end but the array is full. Which approach correctly adds 5 at the end without losing existing data?

hard

A. Overwrite arr[3] with 5 directly

B. Increase size variable to 5 and assign arr[4] = 5

C. Use arr[size] = 5 without resizing

D. Create a new array of size 5, copy old elements, then add 5 at index 4

Solution

1. Step 1: Recognize fixed array size limitation

   Original array size is 4; cannot add element beyond index 3 without resizing.

2. Step 2: Create new larger array and copy elements

   Create new array of size 5, copy existing elements, then insert 5 at index 4.

3. Final Answer:

   Create a new array of size 5, copy old elements, then add 5 at index 4 -> Option D

4. Quick Check:

   Resize by new array and copy before insertion [OK]

Hint: Resize array by copying before adding new element [OK]

Common Mistakes:

• Trying to insert without resizing
• Overwriting last element losing data
• Assuming size variable controls array length