Simplify Java Type Checks: Using Pattern Matching with instanceof in Java 16

The instanceof keyword is used to determine whether an object is an instance of a particular class.

Consider a map where values may be of different types, declared as Object:

Map<String, Object> data = new HashMap<>();
data.put("key1", "aaa");
data.put("key2", 111);

When retrieving a value, you need to check its type before casting. The traditional way:

Object value = data.get("key1");
if (value instanceof String) {
    String s = (String) value;
    System.out.println(s.substring(1));
}

Since Java 16, pattern matching for instanceof allows the type test and cast to be combined:

Object value = data.get("key1");
if (value instanceof String s) {
    System.out.println(s.substring(1));
}

This reduces boilerplate and makes the code clearer.

Tip: The feature went through two preview releases (JDK 14 JEP 305, JDK 15 JEP 375) before being finalized in JDK 16 JEP 394.