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JVM / Java / Basics / Versions

1. Records

Starting with Java 17. No getter, constructor, equals, hashCode. Immutable by default.

 
public class RecordExample {
    public static void main(String[] args) {
        Person p = new Person("John", 20);
        System.out.println(p.name());
        System.out.println(p.age());
        System.out.println(p);
    }
}

record Person(String name, int age) {}  // Java 17

2. Pattern Matching

Starting with Java 17. No explicit cast (less boilerplate). More readable.

 
public class PatternMatchingExample {

    void main() {  // Java 25 (compact main)

        // Java 8
        Object obj = "Hello";
        if (obj instanceof String) {
            String str = (String) obj;
            System.out.println(str.length());
        }

        // Java 17
        Object obj2 = "Hello";
        if (obj2 instanceof String str) {
            System.out.println(str.length());
        }

        // Java 21
        Object obj3 = new Person("Bob", 30);
        if (obj3 instanceof Person(String name, int age)) {
            System.out.println(name + " is " + age);
        }
    }
}

record Person(String name, int age) {}

3. Switch Improvements

Starting with Java 17. No fallthrough bugs. Works with types (Java 21).

 
package versions;

public class SwitchExample {
    void main() { // Java 25

        switchJava8();
        switchJava17();
        switchJava21();
    }

    void switchJava8() { // Java 8
        int day =2;
        String result;

        switch (day) {
            case 1:
                result = "Mon";
                break;
            case 2:
                result = "Tue";
                break;
            default:
                result = "Other";
        }
        
        System.out.println(result);
    }

    void switchJava17() {  // Java 17
        int day = 2;

        // Switch expression
        String result = switch(day) {
            case 1 -> "Mon";
            case 2 -> "Tue";
            default -> "Other";
        };

        System.out.println(result);
    }

    void switchJava21() {  // Java 21
        Object obj = 10;

        // Pattern matching switch
        String result = switch (obj) {
            case Integer i -> "Integer: " + i;
            case String s -> "String: " + s;
            default -> "Unknown";
        };

        System.out.println(result);
    }
}