Pattern Matching in Java 17

Pattern Matching improves type checking and reduces boilerplate code.

Java 17 includes:

• Pattern Matching for instanceof (Finalized)
• Pattern Matching for switch (Preview in Java 17)

It makes type-based logic cleaner and safer.

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Pattern Matching for instanceof

Before Java 16

Object obj = "Hello";

if (obj instanceof String) {
    String s = (String) obj;
    System.out.println(s.length());
}

Problems:

• Repeated type
• Manual casting
• Verbose

After (Java 17)

Object obj = "Hello";

if (obj instanceof String s) {
System.out.println(s.length());
}

What changed?

✔ Automatic type casting
✔ New variable s declared
✔ Cleaner and safer

How It Works

if (obj instanceof String s)

Means:

• Check if obj is String
• If true → bind to variable s
• s is available inside the block

Scope Rules:

if (obj instanceof String s && s.length() > 3) {
System.out.println(s);
}

✔ s is available in condition
✔ s available inside block

Outside block → not accessible.

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Pattern Matching for switch (Preview in Java 17)

Switch can now match types directly.

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Traditional Switch (Old Style)

if (obj instanceof String s) {

System.out.println(s.length());

} else if (obj instanceof Integer i) {

System.out.println(i * 2);

}

Pattern Matching Switch

switch (obj) {

case String s -> System.out.println(s.length());

case Integer i -> System.out.println(i * 2);

default -> System.out.println("Unknown type");

}

Cleaner. More readable.

Limitations in Java 17

• Pattern matching for switch was preview in 17
• Must enable preview features during compilation

Compile with:

–enable-preview

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Pattern matching in Java 17 simplifies type checking by combining instanceof with variable binding and enabling type-based switch expressions.
It reduces casting, improves readability, and works well with sealed classes for safer domain modeling.