Notice: This page requires JavaScript to function properly.
Please enable JavaScript in your browser settings or update your browser.Lernen Introduction to Data Structures | Basic Data Structures
Java Data Structures
course content

Kursinhalt

Java Data Structures

Java Data Structures

1. Basic Data Structures
Introduction to Data StructuresList and ArrayListChallenge: ArrayListCRUD operationsLinkedListImplementing our LinkedListChallenge: LinkedListSection 1 Summary
2. Additional Data Structures
QueueDequeQueue PracticeStackChallenge: Deque PracticeSection 2 Summary
3. Map
What is Map?HashMap<>HashMap PracticeMap with Other Data StructuresSection 3 Summary
4. enum & Stream API
enumChallenge: Character ClassStream APIMethod ReferenceStream PracticeSection 4 Summary

book
Introduction to Data Structures

Welcome to Java Data Structures! This course is tailored for Java developers looking to strengthen their understanding of data structures and boost their coding efficiency.

This course isn't for beginners. If you haven't completed our previous three Java courses, you might find it challenging.

To get the most out of this course, we strongly recommend completing them first before diving into Java Data Structures.

What are Collections, and Why Are They Needed?

Collections in Java are one of the data structures that are used very frequently. A data structure, in turn, is a way of storing various data types.

In simple terms, a collection is a list of data or variables of a specific type.
While arrays are static, meaning they have a fixed size defined during initialization, collections can be thought of as dynamic arrays. They expand as elements are added to them. So, when you add an element to the list, the size of the list increases until it can accommodate all the elements.

Collections can help us understand how a database works because, with collections, we can also store a large amount of data. In collections, we can store objects of different classes. We can even store arrays in collections, which is a very convenient way to store a large amount of data.

Wrappers

To start working with collections, it's worth noting that collections cannot operate with primitive data types. They specifically work with objects. To store a simple number or letter, we need to use a wrapper class for the primitive data type.

Primitive data types (such as int, char, float, boolean, and others) are not objects, and sometimes there's a need to work with them as objects, for example, in collections or when using classes that expect objects. Wrapper classes offer an object-oriented wrapper for each primitive type.

Here's a list of wrapper classes for primitive types:

These classes provide methods for converting between primitive types and objects, as well as various functions for working with values, such as comparison, arithmetic operations, and more.

Let's look at a few examples of using wrapper classes:

java

Main

copy

              
1234567891011

            
package com.example;

public class Main {
    public static void main(String[] args) {
        Integer wrap = 15; // Autoboxing: converting a primitive int to an `Integer` object
        int prim = wrap; // Unboxing: converting an `Integer` object back to a primitive int

        int result = wrap.compareTo(prim); // Using the `compareTo` method of the `Integer` class
        System.out.println(result);
    }
}

In the code above, we created an object of the Integer class and initialized it with a regular number. This is an example of autoboxing. Next, we created a primitive int and assigned it the value of the wrapper, which is called unboxing.

From this, we can understand that autoboxing is the automatic conversion of a primitive data type into an object of the wrapper class. On the other hand, unboxing is the automatic conversion of an object of the wrapper class back to a primitive data type.

You can also see how we used the comparison method, which returns 0 if the values are equal, 1 if the left value is greater than the right, and -1 if the left value is smaller than the right.

Wrapper classes offer many useful methods. We won't cover all of them now, but you can explore them in your IDE.

I suggest practicing a bit by modifying the compareTo() method so that instead of numeric indicators, it returns full-text messages indicating which number is greater:

Aufgabe

Swipe to start coding

You need to handle the result of the compareTo() method so that instead of returning -1, 0, or 1, it returns descriptive text messages.

  1. Implement the upgrade_comparing method.
  2. Use compareTo() to compare values.
  3. Return a string based on the comparison result:
    • If -1 → "The right value is greater".
    • If 0 → "The values are equal".
    • If 1 → "The left value is greater".

Once you've completed this task, click the button below the code to check your solution.

Lösung

java

solution

Switch to desktopWechseln Sie zum Desktop, um in der realen Welt zu übenFahren Sie dort fort, wo Sie sind, indem Sie eine der folgenden Optionen verwenden
War alles klar?

Wie können wir es verbessern?

Danke für Ihr Feedback!

Abschnitt 1. Kapitel 1
toggle bottom row

book
Introduction to Data Structures

Welcome to Java Data Structures! This course is tailored for Java developers looking to strengthen their understanding of data structures and boost their coding efficiency.

This course isn't for beginners. If you haven't completed our previous three Java courses, you might find it challenging.

To get the most out of this course, we strongly recommend completing them first before diving into Java Data Structures.

What are Collections, and Why Are They Needed?

Collections in Java are one of the data structures that are used very frequently. A data structure, in turn, is a way of storing various data types.

In simple terms, a collection is a list of data or variables of a specific type.
While arrays are static, meaning they have a fixed size defined during initialization, collections can be thought of as dynamic arrays. They expand as elements are added to them. So, when you add an element to the list, the size of the list increases until it can accommodate all the elements.

Collections can help us understand how a database works because, with collections, we can also store a large amount of data. In collections, we can store objects of different classes. We can even store arrays in collections, which is a very convenient way to store a large amount of data.

Wrappers

To start working with collections, it's worth noting that collections cannot operate with primitive data types. They specifically work with objects. To store a simple number or letter, we need to use a wrapper class for the primitive data type.

Primitive data types (such as int, char, float, boolean, and others) are not objects, and sometimes there's a need to work with them as objects, for example, in collections or when using classes that expect objects. Wrapper classes offer an object-oriented wrapper for each primitive type.

Here's a list of wrapper classes for primitive types:

These classes provide methods for converting between primitive types and objects, as well as various functions for working with values, such as comparison, arithmetic operations, and more.

Let's look at a few examples of using wrapper classes:

java

Main

copy

              
1234567891011

            
package com.example;

public class Main {
    public static void main(String[] args) {
        Integer wrap = 15; // Autoboxing: converting a primitive int to an `Integer` object
        int prim = wrap; // Unboxing: converting an `Integer` object back to a primitive int

        int result = wrap.compareTo(prim); // Using the `compareTo` method of the `Integer` class
        System.out.println(result);
    }
}

In the code above, we created an object of the Integer class and initialized it with a regular number. This is an example of autoboxing. Next, we created a primitive int and assigned it the value of the wrapper, which is called unboxing.

From this, we can understand that autoboxing is the automatic conversion of a primitive data type into an object of the wrapper class. On the other hand, unboxing is the automatic conversion of an object of the wrapper class back to a primitive data type.

You can also see how we used the comparison method, which returns 0 if the values are equal, 1 if the left value is greater than the right, and -1 if the left value is smaller than the right.

Wrapper classes offer many useful methods. We won't cover all of them now, but you can explore them in your IDE.

I suggest practicing a bit by modifying the compareTo() method so that instead of numeric indicators, it returns full-text messages indicating which number is greater:

Aufgabe

Swipe to start coding

You need to handle the result of the compareTo() method so that instead of returning -1, 0, or 1, it returns descriptive text messages.

  1. Implement the upgrade_comparing method.
  2. Use compareTo() to compare values.
  3. Return a string based on the comparison result:
    • If -1 → "The right value is greater".
    • If 0 → "The values are equal".
    • If 1 → "The left value is greater".

Once you've completed this task, click the button below the code to check your solution.

Lösung

java

solution

Switch to desktopWechseln Sie zum Desktop, um in der realen Welt zu übenFahren Sie dort fort, wo Sie sind, indem Sie eine der folgenden Optionen verwenden
War alles klar?

Wie können wir es verbessern?

Danke für Ihr Feedback!

Abschnitt 1. Kapitel 1
Switch to desktopWechseln Sie zum Desktop, um in der realen Welt zu übenFahren Sie dort fort, wo Sie sind, indem Sie eine der folgenden Optionen verwenden
We're sorry to hear that something went wrong. What happened?
some-alt