How Java 17’s Switch Pattern Matching Simplifies Type Checks

Recently I recorded a video about the instanceof enhancement introduced in Java 16. If you prefer not to watch the video, you can revisit the concept with the following example.

Map<String, Object> data = new HashMap<>();
data.put("key1", "aaa");
data.put("key2", 111);
if (data.get("key1") instanceof String s) {
    log.info(s);
}

In this scenario the values stored in the map have different types, so instanceof is used to determine the runtime type of the retrieved value before processing it. If the map may contain String, Integer or Double, a typical approach would be a chain of if‑else statements:

if (data.get("key") instanceof String s) {
    log.info(s);
} else if (data.get("key") instanceof Double d) {
    log.info(d);
} else if (data.get("key") instanceof Integer i) {
    log.info(i);
}

Such a nested if structure can become cumbersome. Starting with Java 17, the switch statement has been enhanced to support pattern matching, allowing a more concise formulation:

switch (data.get("key1")) {
    case String s  -> log.info(s);
    case Double d  -> log.info(d.toString());
    case Integer i -> log.info(i.toString());
    default         -> log.info("");
}

The key improvements are:

The case label combines type checking and casting, similar to the instanceof enhancement introduced in Java 16.

Each case can be expressed with a lambda‑style arrow, eliminating the need for a break statement (as introduced by the switch expression enhancements in JDK 14).

Note that pattern‑matching for switch expressions is still a preview feature in JDK 17, so it should be used for learning purposes only and not in production code.