Kursusindhold

Java Basics

1. Getting Started

Backend Development Role of Java in the Backend Java Advantages Memory Types In Java Java's Syntax Your First Program Comments

2. Basic Types and Operations

Primitive Data Types Challenge: Primitive Types Mathematical Operations on char Mathematical Operations in Java If-Else Statement Switch-Case Statement New Task Structure Challenge: Weekday Switch

3. Loops

Introduction to Loops While-Loop Do-While Loop Challenge: Building a Server Retry Mechanism For-Loop Increment and Decrement Infinite Loop Challenge: Filtering Numbers in a Loop

4. Arrays

What is Array?Using Loops with Arrays Index Out Of Bounds Two-Dimentional Array Iteration In Two-Dimensional Array For-Each Loop

5. String

What Is String? Basic Methods In String Practical Applications of String Methods Challenge: Filter Failure Messages NullPointerException StringBuilder String Pool, Method Equals() Summary

Iteration In Two-Dimensional Array

How to iterate inside two-dimensional array using a for-loop?

Iterating through a two-dimensional array can be a bit challenging to grasp initially, so don't worry if it doesn't click right away. In this chapter, I'll demonstrate how to do it and explain how it functions.

We use a nested loop to iterate through a two-dimensional array, meaning one loop inside another. The outer loop iterates over the rows, while the inner loop iterates over the columns. Let's examine the syntax for iterating through a two-dimensional array using the example array we created in the previous chapter:

Main


              12345678910111213141516
            
package com.example;

public class Main {
    public static void main(String[] args) {
        int[][] twoDimensionalArray = { {1, 2, 3, 4},
                                        {5, 6, 7, 8},
                                        {9, 10, 11, 12},
                                        {13, 14, 15, 16} };
        for (int i = 0; i < twoDimensionalArray.length; i++) {
            for (int j = 0; j < twoDimensionalArray[0].length; j++) {
                System.out.print(twoDimensionalArray[i][j] + " ");
            }
            System.out.println();
        }
    }
}

Let's delve into the meaning of each element in the code snippet provided above:

int[][] twoDimensionalArray =: this line initializes a two-dimensional array;
for (int i = 0; i < twoDimensionalArray.length; i++): the first for-loop iterates over the rows of our matrix. While we're on the first row, our program enters the nested loop, which doesn't impact the outer loop. The variable i represents the current row number;
for (int j = 0; j < twoDimensionalArray[0].length; j++): the second for-loop iterates over the columns of the matrix. While we're on the 0th row, we iterate through the columns of that row. The variable j represents the current column number;
System.out.print(twoDimensionalArray[i][j] + " "): in this line, we use System.out.print to display our values in a single line. Let's see how it operates: while we're on the 0th row, we iterate through the columns on that row. For example, array[0][1], followed by array[0][2], and so on. We continue through the columns as long as j is less than array[0].length. Once we reach array[0].length, we return to the outer array and move to the first row. For example, array[0][3] -> array[1][0]. We've reached our boundaries and then transitioned to row 1.

Opgave

Swipe to start coding

Calculate the average temperature for each day of the week based on data from multiple stations.

You are given:

Station 1: {20, 22, 24, 19, 21, 23, 25}
Station 2: {18, 20, 22, 19, 20, 22, 24}
Station 3: {21, 23, 25, 22, 24, 26, 28}
Station 4: {19, 21, 23, 20, 22, 24, 26}

Your job:

Write a method called calculateDailyAverages(int[][] temperatures) that returns a double[].
In this method:
- Loop through each day (columns of the 2D array).
- For each day, initialize totalTemp to store the sum of temperatures.
- Use an inner loop to go through all stations (rows).
- Sum the temperatures from each station for the current day.
- Divide the total by the number of stations to get the average.
- Store the result in an array.
Return the array of averages.

Løsning

solution

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Sektion 4. Kapitel 5

Iteration In Two-Dimensional Array

How to iterate inside two-dimensional array using a for-loop?

Main


              12345678910111213141516
            
package com.example;

public class Main {
    public static void main(String[] args) {
        int[][] twoDimensionalArray = { {1, 2, 3, 4},
                                        {5, 6, 7, 8},
                                        {9, 10, 11, 12},
                                        {13, 14, 15, 16} };
        for (int i = 0; i < twoDimensionalArray.length; i++) {
            for (int j = 0; j < twoDimensionalArray[0].length; j++) {
                System.out.print(twoDimensionalArray[i][j] + " ");
            }
            System.out.println();
        }
    }
}

Let's delve into the meaning of each element in the code snippet provided above:

int[][] twoDimensionalArray =: this line initializes a two-dimensional array;
for (int i = 0; i < twoDimensionalArray.length; i++): the first for-loop iterates over the rows of our matrix. While we're on the first row, our program enters the nested loop, which doesn't impact the outer loop. The variable i represents the current row number;
for (int j = 0; j < twoDimensionalArray[0].length; j++): the second for-loop iterates over the columns of the matrix. While we're on the 0th row, we iterate through the columns of that row. The variable j represents the current column number;
System.out.print(twoDimensionalArray[i][j] + " "): in this line, we use System.out.print to display our values in a single line. Let's see how it operates: while we're on the 0th row, we iterate through the columns on that row. For example, array[0][1], followed by array[0][2], and so on. We continue through the columns as long as j is less than array[0].length. Once we reach array[0].length, we return to the outer array and move to the first row. For example, array[0][3] -> array[1][0]. We've reached our boundaries and then transitioned to row 1.

Opgave

Swipe to start coding

Calculate the average temperature for each day of the week based on data from multiple stations.

You are given:

Station 1: {20, 22, 24, 19, 21, 23, 25}
Station 2: {18, 20, 22, 19, 20, 22, 24}
Station 3: {21, 23, 25, 22, 24, 26, 28}
Station 4: {19, 21, 23, 20, 22, 24, 26}

Your job:

Write a method called calculateDailyAverages(int[][] temperatures) that returns a double[].
In this method:
- Loop through each day (columns of the 2D array).
- For each day, initialize totalTemp to store the sum of temperatures.
- Use an inner loop to go through all stations (rows).
- Sum the temperatures from each station for the current day.
- Divide the total by the number of stations to get the average.
- Store the result in an array.
Return the array of averages.

Løsning

solution

Skift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder

Var alt klart?

Tak for dine kommentarer!

Sektion 4. Kapitel 5

Skift til skrivebord for at øve i den virkelige verdenFortsæt der, hvor du er, med en af nedenstående muligheder