Oppiskele Wrapper Classes and Autoboxing | Type Conversion and Wrapper Classes

In Java, primitive types such as int, double, and char are not objects and therefore do not inherit from Object or provide methods. However, Java offers wrapper classes for all primitive types, allowing you to treat primitive values as objects. The main wrapper classes are Integer for int, Double for double, Character for char, and so on. These wrapper classes enable primitives to be used in contexts that require objects, such as collections like ArrayList, and provide utility methods for parsing, converting, and comparing values.

Wrapper classes are particularly useful when you need to store primitive values in data structures that only accept objects, or when you want to take advantage of the methods available on these classes. For example, the Integer class provides methods like parseInt, compareTo, and toString. Java automatically handles conversion between primitives and their corresponding wrapper types through a process called autoboxing (converting a primitive to a wrapper) and unboxing (converting a wrapper to a primitive). This feature simplifies code and reduces the need for manual conversions.

Main.java


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package com.example;
import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        // Autoboxing: primitive int to Integer object
        Integer wrappedInt = 42; // Java automatically wraps the int

        // Unboxing: Integer object to primitive int
        int primitiveInt = wrappedInt; // Java automatically unwraps the Integer

        // Using wrapper objects in a collection
        ArrayList<Double> numbers = new ArrayList<>();
        numbers.add(3.14); // Autoboxing double to Double
        numbers.add(2.71);

        // Retrieving and unboxing
        double first = numbers.get(0); // Unboxing Double to double

        System.out.println("Wrapped int: " + wrappedInt);
        System.out.println("Primitive int: " + primitiveInt);
        System.out.println("Numbers: " + numbers);
        System.out.println("First number as double: " + first);
    }
}

1. Which of the following situations in Java will trigger autoboxing?

2. What is the main difference between using `==` and `.equals()` with wrapper objects like `Integer` or `Double`?

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Osio 3. Luku 2

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Can you give examples of how to use wrapper classes in Java?

What is autoboxing and unboxing in more detail?

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Main.java


              12345678910111213141516171819202122232425
            
package com.example;
import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {
        // Autoboxing: primitive int to Integer object
        Integer wrappedInt = 42; // Java automatically wraps the int

        // Unboxing: Integer object to primitive int
        int primitiveInt = wrappedInt; // Java automatically unwraps the Integer

        // Using wrapper objects in a collection
        ArrayList<Double> numbers = new ArrayList<>();
        numbers.add(3.14); // Autoboxing double to Double
        numbers.add(2.71);

        // Retrieving and unboxing
        double first = numbers.get(0); // Unboxing Double to double

        System.out.println("Wrapped int: " + wrappedInt);
        System.out.println("Primitive int: " + primitiveInt);
        System.out.println("Numbers: " + numbers);
        System.out.println("First number as double: " + first);
    }
}

1. Which of the following situations in Java will trigger autoboxing?

2. What is the main difference between using `==` and `.equals()` with wrapper objects like `Integer` or `Double`?

Oliko kaikki selvää?

Kiitos palautteestasi!

Osio 3. Luku 2

Wrapper Classes and Autoboxing

1. Which of the following situations in Java will trigger autoboxing?

2. What is the main difference between using == and .equals() with wrapper objects like Integer or Double?

Awesome!

Wrapper Classes and Autoboxing

1. Which of the following situations in Java will trigger autoboxing?

2. What is the main difference between using == and .equals() with wrapper objects like Integer or Double?

2. What is the main difference between using `==` and `.equals()` with wrapper objects like `Integer` or `Double`?

2. What is the main difference between using `==` and `.equals()` with wrapper objects like `Integer` or `Double`?