How to get screen resolution (screen size) using Java?

Question:

How to get screen resolution (screen size) using Java?

Code:

import java.awt.*;
 
public class GetScreenSize {
 
  public static void main(String[] args) {
 
    Dimension screen = Toolkit.getDefaultToolkit().getScreenSize();
    System.out.println("Height: " + screen.height);
    System.out.println("Width: " + screen.width);
 
  }
}

Output:

$ java GetScreenSize
Height: 1200
Width: 1920

Counting vowels in a java string?

Question:

How to count vowels in a string?
How to count upper case vowels in a string?
How to count lower case vowels in a string?

Code:

public class CountVowels {
  public static void main(String[] args) {
 
    String str = "abcdefg HIJKLMNOP qrstuvwxyz";
 
    int upper = 0;
    int lower = 0;
    int non = 0;
 
    String vowels = "aeiouAEIOU";
    char[] array = str.toCharArray();
 
    for(char c: array) {
      if(vowels.indexOf(c) != -1){
        if(Character.isLowerCase(c)){
          lower = lower + 1;
        } else if(Character.isUpperCase(c)){
          upper = upper + 1;
        }
      } else {
         non = non + 1;
      }
    }
    System.out.println("String: " + str);
    System.out.println("Upper case vowels: " + upper);
    System.out.println("Lower case vowels: " + lower);
    System.out.println("Non vowels: " + non);
  }
}

Output:

$ java CountVowels
String: abcdefg HIJKLMNOP qrstuvwxyz
Upper case vowels: 2
Lower case vowels: 3
Non vowels: 23

Creating a celsius to fahrenheit calculator using a JSlider.

Question:

Create a celsius to fahrenheit calculator using a JSlider.

Code:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.event.*;
 
public class CelsiusToFahrenheit {
 
  public static void main(String[] arguments) {
 
    JFrame.setDefaultLookAndFeelDecorated(true);
    JFrame f = new JFrame("Celsius To Fahrenheit");
    f.setSize(400,200);
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
    JPanel container = new JPanel();
    container.setBorder(BorderFactory.createEmptyBorder(0,20,0,20));
    container.setLayout(new GridLayout(3, 1));
 
    JPanel results = new JPanel();
    results.setLayout(new FlowLayout());
 
    JLabel cLabel = new JLabel("Celsius: ");
    final JTextField cText = new JTextField(5);
 
    JLabel fLabel = new JLabel("Fahrenheit: ");
    final JTextField fText = new JTextField(5);
    results.add(cLabel);
    results.add(cText);
    results.add(fLabel);
    results.add(fText);
 
 
    JLabel sLabel = new JLabel("Celsius Slider",JLabel.CENTER);
    final JSlider slider = new JSlider(JSlider.HORIZONTAL,0,100,10);
    slider.setMinorTickSpacing(5);  
    slider.setMajorTickSpacing(20);  
    slider.setPaintTicks(true);  
    slider.setPaintLabels(true);  
 
 
    slider.addChangeListener(new ChangeListener() {
      public void stateChanged(ChangeEvent e) {
        int c = slider.getValue();
        fText.setText("" + (c * (double) 9 / 5 + 32) );
        cText.setText("" + c);
      }
    });
 
    // set default value
    fText.setText("" + (slider.getValue() * (double) 9 / 5 + 32) );
    cText.setText("" + slider.getValue());
 
    container.add(sLabel);
    container.add(slider);
    container.add(results);
 
    f.add(container);
    f.setVisible(true);
 
  }
}
 

Output:

Drawing a Rectangle using astrisks

Question:

How to write a java program that will ask for the length and width of a rectangle and then multiply them together and create a rectangle out of astrisks?

Code:

import java.util.Scanner;
 
public class Rectangle {
 
  public static void main(String[] args) {
 
    Scanner sc = new Scanner(System.in);
 
    System.out.print("Enter height: ");
    int h = sc.nextInt();
 
    System.out.print("Enter width: ");
    int w = sc.nextInt();
 
    for(int i=0;i<h;i++){
      for(int j=0;j<w;j++){
        System.out.print("*");
      }
      System.out.println();
    }
  }
}

Output:

$ java Rectangle
Enter height: 5
Enter width: 20
********************
********************
********************
********************
********************

m(i)=1/3 + 2/5 +...+ i/(2i+i)

Question:

java program to solve: 

  m(i)=1/3 + 2/5 +...+ i/(2i+i)

Answer:

Use recursion

Code:

import java.util.Scanner;
 
public class Example {
 
   public static void main(String[] args) {
      Scanner input = new Scanner(System.in);
      System.out.print("Enter a value: ");
      int n = input.nextInt();
 
      double d = m(n);
      System.out.println("m(5) = " + d );
   }
 
   public static double m(int i) {
      double d = (double)i/(2*i+1);
      if(i <= 1){
        return(d);
      } else {
        return (d + m(i-1));
      }
   }
}

Output:

$ java Example
Enter a value: 5
m(5) = 2.060894660894661

Create ArrayList (ArrayList) from array (T[])

Question:

I have an array that is initialized like:
  Element[] array = {new Element(1), new Element(2), new Element(3)};

I would like to convert this array into an object of the ArrayList class:
  ArrayList arraylist = ???;

Answer:

new ArrayList(Arrays.asList(array))

Code:

import java.util.*;
 
public class ArrayToArrayList {
 
  public static void main(String[] args) {
 
    String[] array = {new String("aaa"),new String("bbb"),new String("ccc")};
 
    ArrayList<String> list = new ArrayList<String>(Arrays.asList(array));
 
    System.out.println("array: " + Arrays.toString(array));
    System.out.println("list: " + list);
 
  }
}

Output:

$ java ArrayToArrayList
array: [aaa, bbb, ccc]
list: [aaa, bbb, ccc]

How do I convert int[] into List in Java?

Question:

How do I convert int[] into List in Java?

Code:

import java.util.*;
 
public class IntToList {
 
  public static void main(String[] args) {
 
    int[] ints = new int[]{1,2,3,4,5,6,7,8,9};
 
    List<Integer> list = new ArrayList<Integer>();
    for (int n = 0; n < ints.length; n++) {
        list.add(ints[n]);
    }
 
    System.out.println("int[] ints: " + Arrays.toString(ints));
 
 
    System.out.print("List<Integer> list: ");
    for(int i=0;i<list.size();i++){
      System.out.print(list.get(i) + " ");
    }
    System.out.println();
  }
}

Output:

$ java IntToList
int[] ints: [1, 2, 3, 4, 5, 6, 7, 8, 9]
List list: 1 2 3 4 5 6 7 8 9