Pattern Matching

Part of the Logic & Flow section of Coddy's Java journey — lesson 37 of 59.

Pattern matching in Java allows you to test if an object has a specific type and extract components from it. It simplifies type checking and casting operations.

Let's see how to use pattern matching with instanceof:

Object obj = "Hello";
if (obj instanceof String str) {
   // str is automatically cast to String
   System.out.println(str.toUpperCase());
}

After executing the above code, the output is:

"HELLO"

You can also use pattern matching in switch expressions:

Object value = 42;
String result;
if (value instanceof Integer i) {
    result = "Number: " + i;
} else if (value instanceof String s) {
    result = "Text: " + s;
} else {
    result = "Unknown";
}

After executing the above code, result contains:

“Number: 42”

Challenge

Easy

Create a method named processValue that takes one argument:

An Object (value) that could be of different types

The method should use pattern matching with instanceof to process the value and return a string based on these rules:

If it's an Integer: return "Number: " followed by the value doubled
If it's a String: return "Text: " followed by the value in uppercase
If it's a Boolean: return "Boolean: " followed by the opposite value (true becomes false and vice versa)
For any other type: return "Unknown"

Cheat sheet

Pattern matching in Java allows you to test if an object has a specific type and extract components from it using instanceof:

Object obj = "Hello";
if (obj instanceof String str) {
   // str is automatically cast to String
   System.out.println(str.toUpperCase());
}

You can chain multiple pattern matching checks:

Object value = 42;
String result;
if (value instanceof Integer i) {
    result = "Number: " + i;
} else if (value instanceof String s) {
    result = "Text: " + s;
} else {
    result = "Unknown";
}

Try it yourself

import java.util.Scanner;

public class Main {
    public static String processValue(Object value) {
        // TODO: Use pattern matching with instanceof to process the value
        // If it's an Integer: return "Number: " + (value * 2)
        // If it's a String: return "Text: " + value.toUpperCase()
        // If it's a Boolean: return "Boolean: " + (!value)
        // For any other type: return "Unknown"
        
    }
    
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String type = scanner.nextLine();
        String inputValue = scanner.nextLine();
        
        Object value = switch(type) {
            case "Integer" -> Integer.parseInt(inputValue);
            case "String" -> inputValue;
            case "Boolean" -> Boolean.parseBoolean(inputValue);
            default -> inputValue;
        };
        
        System.out.println(processValue(value));
    }
}