Java Coding Interview Preparation

Progress:

• Clarify requirements (2-3 minutes)
• Design approach (3-5 minutes)
• Write test cases first (5-7 minutes)
• Implement solution (15-20 minutes)
• Test and refine (5-10 minutes)
• Discuss trade-offs (remaining time)

Step 1: Requirements Clarification

Ask specific questions:

• Input constraints (size, range, null handling)
• Expected output format
• Edge cases behavior
• Performance requirements

Step 2: Design Approach

Verbalize your thinking:

Java
/**
 * Approach: Two-pointer technique
 * Time: O(n), Space: O(1)
 * 
 * Key insight: Since array is sorted, we can use
 * left/right pointers moving toward center.
 */

Step 3: Test-Driven Development

Write tests before implementation:

Java
@Test
void testNormalCase() {
    Solution solution = new Solution();
    assertEquals(Arrays.asList(0, 1), solution.twoSum(new int[]{2, 7, 11, 15}, 9));
}

@Test 
void testEdgeCases() {
    Solution solution = new Solution();
    assertThrows(IllegalArgumentException.class, 
        () -> solution.twoSum(null, 9));
    assertTrue(solution.twoSum(new int[]{}, 9).isEmpty());
}

Step 4: Clean Implementation

Java
public class Solution {
    public List<Integer> twoSum(int[] nums, int target) {
        if (nums == null) {
            throw new IllegalArgumentException("Array cannot be null");
        }
        
        Map<Integer, Integer> numToIndex = new HashMap<>();
        
        for (int i = 0; i < nums.length; i++) {
            int complement = target - nums[i];
            
            if (numToIndex.containsKey(complement)) {
                return Arrays.asList(numToIndex.get(complement), i);
            }
            
            numToIndex.put(nums[i], i);
        }
        
        return Collections.emptyList();
    }
}

Code Quality:

• Use meaningful variable names (targetIndex not idx)
• Add javadoc for complex logic
• Handle edge cases explicitly
• Follow Java naming conventions

Problem Solving:

• Start with brute force, then optimize
• Explain time/space complexity
• Consider alternative approaches
• Think about scalability

Communication:

• Vocalize your thought process
• Explain trade-offs ("HashMap gives O(1) lookup but uses O(n) space")
• Ask for feedback during implementation
• Stay calm under pressure

Testing Strategy:

Java
// Cover these test categories:
@Test void testHappyPath() { /* normal input */ }
@Test void testEdgeCases() { /* empty, null, boundary */ }
@Test void testErrorConditions() { /* invalid input */ }
@Test void testPerformance() { /* large inputs if relevant */ }

Don't:

• Jump into coding immediately without clarifying requirements
• Ignore edge cases (null, empty, single element)
• Write overly complex solutions for simple problems
• Forget to test your solution before declaring it complete
• Use obscure Java features that might confuse interviewers

Avoid:

• Raw types: List list = new ArrayList() → List<String> list = new ArrayList<>()
• Mutable static fields
• Catching generic Exception
• Not explaining your reasoning
• Getting stuck on optimization before having working solution

Time Management:

• Don't spend 15 minutes on perfect variable names
• If stuck, ask for hints rather than struggle silently
• Focus on correctness first, optimization second
• Save 5 minutes for testing and discussion