✅ What is a String Template in Java 21?
A String Template is a structured way to define a string with embedded expressions, which are evaluated and inserted in a safe and readable way. It improves code clarity and avoids issues like manual escaping or mistakes in formatting.
✔️ Syntax Example of String Template (Java 21)
String name = "Ashish";
int age = 30;
String result = STR."My name is \{name} and I am \{age} years old.";
System.out.println(result);
STR."..."is a string template literal.- Inside the template, expressions are written as
\{expression}. - At compile-time, these expressions are evaluated and injected into the string.
✅ Advantages of String Templates
| Feature | Benefit |
|---|---|
| Easier Syntax | Cleaner and readable syntax compared to concatenation or String.format(). |
| Compile-Time Safety | Errors in embedded expressions are caught at compile time. |
| Automatic Escaping | No need to manually handle escaping of quotes or special characters. |
| Structured Formatting | Ideal for complex multi-line templates. |
✔️ Example Compared to Earlier Approaches
➤ Pre-Java 21 (Traditional way):
String name = "Ashish";
int age = 30;
// Using concatenation
String result1 = "My name is " + name + " and I am " + age + " years old.";
// Using String.format
String result2 = String.format("My name is %s and I am %d years old.", name, age);
System.out.println(result1);
System.out.println(result2);
➤ Java 21 String Template Way:
String name = "Ashish";
int age = 30;
String result = STR."My name is \{name} and I am \{age} years old.";
System.out.println(result);
✅ Key Differences Between String Template and Earlier Approaches
| Aspect | Pre-Java 21 | Java 21 String Template |
|---|---|---|
| Syntax | Verbose (concatenation, String.format) | Cleaner and easier to read |
| Safety | Runtime errors if format string is wrong | Compile-time checks |
| Escaping | Manual, error-prone | Handled automatically |
| Performance | Moderate, because of repeated concatenations | Efficient at compile time |
| Multi-line strings | Complicated, need workarounds | Supported naturally with templates |
| Reusability | Harder | Templates can be reusable components |
✅ When to Prefer String Templates?
- For dynamic string generation in a readable and safe way.
- When working with multi-line strings (e.g., generating HTML or JSON templates).
- When avoiding manual concatenation and improving code maintainability.
⚠️ Important Note
- String Templates in Java 21 are still in Preview Mode.
- You need to enable preview features to use them:
javac --enable-previewandjava --enable-preview.
✅ Conclusion
String Templates in Java 21 represent a modern, safe, and clean way of working with dynamic strings compared to the older cumbersome ways. It simplifies code, reduces bugs, and improves readability.
Let me know if you want me to provide a detailed blog-style explanation with examples and use-cases.
