Forem: Praven Kumar

💡 Java Streams – Find First Non-Repeating Character

Praven Kumar — Fri, 10 Apr 2026 16:55:26 +0000

Input: Programming
Output: P
🔹 Step 1: Convert String to Character Stream
.word.chars()->Converts the string into an IntStream (ASCII values of characters)
🔹 Step 2: Convert int → Character
.mapToObj(ch -> (char) ch)
Converts each ASCII value into a Character object
🔹 Step 3: Group and Count Characters
.collect(groupingBy(Function.identity(), counting()))
Groups characters by themselves
Counts how many times each character appears
📌 Example Output:
{a=2, b=1, c=1}
🔹 Step 4: Filter Non-Repeating Characters
.filter(entry -> entry.getValue() == 1)
Keeps only characters that appear once
🔹 Step 5: Extract Keys (Characters)
.map(Map.Entry::getKey)
🔹 Step 6: Get First Non-Repeating Character
.findFirst().get();
Returns the first unique character

🔍 Finding Missing Numbers in an Array using Java Streams

Praven Kumar — Mon, 06 Apr 2026 03:11:58 +0000

Input: [1,2,1,2,5,8]
Output: [3,4,6,7]
🧠 Approach:
1️⃣ Find minimum and maximum values
2️⃣ Store elements in a Set for fast lookup
3️⃣ Generate range between min and max
4️⃣ Filter out numbers that are not present
❓ Why rangeClosed() and not range()?
IntStream.range(start, end) → excludes end value
IntStream.rangeClosed(start, end) → includes end value
👉 Example:
range(1, 5) → 1,2,3,4
rangeClosed(1, 5) → 1,2,3,4,5
💡 Since we want to check all numbers from min to max (inclusive),
we use rangeClosed(min, max).

🚀 Java Streams – Separate Even & Odd Numbers in One Line! Ever wondered how to split a list into even and odd numbers using Java Streams?

Praven Kumar — Sun, 05 Apr 2026 10:20:33 +0000

🤔
✅ Approach 1: Using partitioningBy
🧠 Key Point:
.Splits into only 2 groups (true / false)
.Best when condition is boolean
✅ Approach 2: Using groupingBy
🧠 Key Point:
.Allows custom grouping (Even / Odd)
.More flexible than partitioning

Join a list of strings with '[' as prefix, ']' as suffix, and ',' as delimiter using streams.

Praven Kumar — Sat, 04 Apr 2026 13:53:22 +0000

Step 1: Convert List → Stream -> languageList.stream()
Step 2: Collecting using joining()
Collectors.joining(delimiter, prefix, suffix)->.collect(Collectors.joining(",", "[", "]"))

𝐂𝐨𝐥𝐥𝐞𝐜𝐭𝐨𝐫𝐬.𝐣𝐨𝐢𝐧𝐢𝐧𝐠(",", "[", "]") 𝐣𝐨𝐢𝐧𝐬 𝐭𝐡𝐞 𝐞𝐥𝐞𝐦𝐞𝐧𝐭𝐬 𝐨𝐟 𝐚 𝐬𝐭𝐫𝐞𝐚𝐦 𝐢𝐧𝐭𝐨 𝐚 𝐬𝐢𝐧𝐠𝐥𝐞 𝐒𝐭𝐫𝐢𝐧𝐠, 𝐬𝐞𝐩𝐚𝐫𝐚𝐭𝐞𝐝 𝐛𝐲 𝐚 𝐜𝐨𝐦𝐦𝐚, 𝐚𝐧𝐝 𝐚𝐝𝐝𝐬 [ 𝐚𝐭 𝐭𝐡𝐞 𝐛𝐞𝐠𝐢𝐧𝐧𝐢𝐧𝐠 𝐚𝐧𝐝 ] 𝐚𝐭 𝐭𝐡𝐞 𝐞𝐧𝐝.