Скачать или смотреть ✂️ Slice It Right! Mastering substring() in Java

Ever wanted to grab just part of a string? Whether you're pulling out names, file extensions, or keywords — Java’s substring() method is the tool for the job. Let’s break it down!

🧱 Step 1: Start with a String
We begin with a simple string:
JavaProgramming

This is a combination of two words: "Java" and "Programming" — great for slicing!

🎯 Goal: Extract specific parts of this string using substring(startIndex, endIndex) — where startIndex is inclusive and endIndex is exclusive.

🪓 Step 2: Extract a Word in the Middle
We pull out a part of the string starting from index 4 to index 10. That gives us:
➡️ "Program" — the first 7 letters of "Programming"

📌 Important: substring(4, 10) includes index 4 but stops before index 10.

🔤 Step 3: Extract the Beginning
Let’s grab the first word: "Java"
That means we slice from index 0 to 4.

✂️ A common use: Extracting a first name or file prefix.

🧭 Step 4: From Index to End
Now we extract everything from index 4 to the end of the string.
Result: "Programming"

🧪 Usage: Helpful when you know where your data starts, but not where it ends.

🔁 Step 5: Get the Whole String Back
You can actually use substring(0, fullLength) to recreate the full string.
Yes, it’s the same as the original.

🤓 Just because you can doesn’t mean you should — but it’s good to know!

⚠️ Step 6: Be Safe with Indexes!
Let’s say you try to slice from index 5 to 50... but the string isn’t that long.
If you're not careful, this throws a StringIndexOutOfBoundsException.

✅ Solution: Check if:

start = 0

end = text.length()

start end

Only then is it safe to extract.

🛡️ Pro tip: Always validate your indices — especially if the substring range is dynamic (e.g., user input or data from a file).

🔍 Step 7: Get a Single Character (Substring Style)
You can simulate charAt(index) using substring(index, index + 1).
For example: extract the character at position 6.

✨ This returns a string, not a char — great for string manipulation or display formatting.

✅ Quick Recap: When to Use substring()
🎯 Extract specific portions of a string

🪪 Slice names, IDs, domains, tags, etc.

📊 Use it for string-based data parsing

🚫 Avoid runtime errors with proper index checks

🔄 Even simulate single-character extraction with a twist!

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