Java related published Questions

      // Method 1: Using String object

      char[] ch = {'g', 'o', 'o', 'd', ' ', 'm', 'o', 'r', 'n', 'i', 'n', 'g'};

      String str = new String(ch);

      System.out.println(str);

<p>Hello World </p>

public enum AlertLevel {

    Undefined(0),

    Ok(1),

    Warning(2),

    Alarm(3);

}

long l = 12345L;

//deprecated from Java 9, use valueOf for better performance

String str = new Long(l).toString(); // str is '12345'

Timer()

Creates a new timer.

​

Timer(boolean isDaemon)

Creates a new timer whose associated thread may be specified to Thread#setDaemon.

​

Timer(String name)

Creates a new timer whose associated thread has the specified name.

​

Timer(String name, boolean isDaemon)

Creates a new timer whose associated thread has the specified name, and may be specified to Thread#setDaemon.

int[] theNumbers = new int[5];

arr[0] = 4;

arr[1] = 8;

arr[2] = 15;

arr[3] = 16;

arr[4] = 23;

arr[5] = 42;

javac MyFisrtProgam.java // enter to compile 

  java MyfirstProgram // run program 

return Math.random() < 0.5;

sudo apt install openjdk-8-jdk

Method overloading is providing two separate methods in a class with the same name but different arguments, while the method return type may or may not be different, which allows us to reuse the same method name.

Method overriding means defining a method in a child class that is already defined in the parent class with the same method signature, same name, arguments, and return type

LinearLayout layout = setupLayout();

int count = layout.getChildCount();

View v = null;

for(int i=0; i<count; i++) {

    v = layout.getChildAt(i);

    //do something with your child element

}

List<Element> list = Arrays.asList(array);

Delete these generated files:

.idea/gradle.xml

.idea/workspace.xml

then click try again to sync the project.

Use ArrayList XD

import java.util.ArrayList;

array.remove(i); //remove element by index

DecimalFormat df = new DecimalFormat();

df.setMaximumFractionDigits(2);

System.out.println(df.format(decimalNumber));

    String a = abc;

    String b = anthony;

    char c = a.charAt(0);

    b.contains(" + c);

    b.contains(String.valueOf(c));

class Main {

    public static void main (String[] args) throws IOException{

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));

        String[] str = br.readLine().split( );      // 6 2

        String[] input = br.readLine().split( );   // 1 2 3 4 5 6

        int n = Integer.parseInt(str[0]);  // 6

        int k = Integer.parseInt(str[1]);  // 2

        int [] arr = new int [n];

        for(int i=0; i<n; i++) 

        {

         arr[i] = Integer.parseInt(input[i]);  // 1 2 3 4 5 6

        }

    }

}

import static org.junit.jupiter.api.Assertions.assertEquals;

import org.junit.jupiter.api.Test;

public class MyTests {

    @Test

    public void multiplicationOfZeroIntegersShouldReturnZero() {

        MyClass tester = new MyClass(); // MyClass is tested

        // assert statements

        assertEquals(0, tester.multiply(10, 0), 10 x 0 must be 0);

        assertEquals(0, tester.multiply(0, 10), 0 x 10 must be 0);

        assertEquals(0, tester.multiply(0, 0), 0 x 0 must be 0);

    }

}

String withSpaces =   Hi  ;

String withoutSpaces = withSpaces.trim();

// Before java 7 - syntax Java catch multiple exceptions and rethrow exception

try

{

   // code that throw exceptions 1 and 3

}

catch(SQLException e)

{

   logger.log(e);

}

catch(IOException e)

{

   logger.log(e);

}

catch(Exception e)

{

   logger.severe(e);

}

new java.util.Timer().schedule( 

        new java.util.TimerTask() {

            @Override

            public void run() {

                // your code here

            }

        }, 

        5000 

);

public static void BubbleSortShortSC(int[] array)

    {

        for(int i = 0; i < array.length - 1; i++)

        {

            boolean sorted = true;

            for (int j = 0; j < array.length - i - 1; j++)

            {

                if(array[j] < array[j+1])

                {

                    int temp = array[j];

                    array[j] = array[j+1];

                    array[j+1] = temp;

                    sorted = false;

                }

            }

            if (sorted)

                break;

        }

    }

<uses-permission android:name=android.permission.INTERNET/>

<application>

    <activity android:name=.activities.MyActivity

        android:permission=android.permission.INTERNET />

</application>

Math.log10()

CriteriaQuery<DeptEmployee> criteriaQuery = 

  criteriaBuilder.createQuery(DeptEmployee.class);

Root<DeptEmployee> root = criteriaQuery.from(DeptEmployee.class);

In<String> inClause = criteriaBuilder.in(root.get(title));

for (String title : titles) {

    inClause.value(title);

}

criteriaQuery.select(root).where(inClause);

android:visibility=gone

//Send value from HomeActivity

val intent = Intent(this@HomeActivity,ProfileActivity::class.java)

intent.putExtra(Username,John Doe)

startActivity(intent)

//Get values in ProfileActivity

val profileName=intent.getStringExtra(Username)

<?xml version=1.0 encoding=utf-8?>

<LinearLayout

    xmlns:android=http://schemas.android.com/apk/res/android

    android:layout_width=match_parent

    android:layout_height=wrap_content

    android:orientation=horizontal

    android:padding=10dp>

    <TextView

        android:id=@+id/tvAnimalName

        android:layout_width=wrap_content

        android:layout_height=wrap_content

        android:textSize=20sp/>

</LinearLayout>

//Occurs when trying to remove an element from a Collection

//while iterating over it

//Where removal takes place

//Setup an iterator

Iterator<Thing> iter = things.iterator();

//Iterate over collection

while(iter.hasNext()) {

    Thing thing = iter.next();

    if (/* Some Condition that initiates removal */) {

      //Remove using iterator

      iter.remove();

    }

}

//Avoids ConcurrentModificationException

Arrays.sort(myArr, (a, b) -> a[0] - b[0]);

public static void main(String[] args){

    System.out.println(Hello World); 

}

int sprintf(char *str, const char *format, ...)

​

Parameters:

​

str − This is the pointer to an array of char elements where the resulting C string is stored.

​

format − This is the String that contains the text to be written to buffer. It can optionally contain embedded format tags that are replaced by the values specified in subsequent additional arguments and formatted as requested. Format tags prototype: %[flags][width][.precision][length]specifier

​

EXAMPLE:

​

#include <stdio.h>

#include <math.h>

​

int main () {

   char str[80];

​

   sprintf(str, "Value of Pi = %f", M_PI);

   puts(str);

   return(0);

}

​

OUTPUT:

​

Value of Pi = 3.141593

//resource

Drawable unwrappedDrawable = AppCompatResources.getDrawable(context, R.drawable.my_drawable); 

Drawable wrappedDrawable = DrawableCompat.wrap(unwrappedDrawable);

DrawableCompat.setTint(wrappedDrawable, Color.RED);    

//activity

Drawable unwrappedDrawable = tvContinue.getBackground();

Drawable wrappedDrawable = DrawableCompat.wrap(unwrappedDrawable);

DrawableCompat.setTint(wrappedDrawable, (Color.parseColor(getPreferences().getString(Constant.SECOND_COLOR, Constant.SECONDARY_COLOR))));

//adapter

Drawable unwrappedDrawable = holder.tvOff.getBackground();

 Drawable wrappedDrawable = DrawableCompat.wrap(unwrappedDrawable);

 DrawableCompat.setTint(wrappedDrawable, (Color.parseColor(((BaseActivity) activity).getPreferences().getString(Constant.SECOND_COLOR, Constant.SECONDARY_COLOR))));

//

getSupportActionBar().hide();

class java

{ 

  public static void main()

  {

    system.out.println(leave it);

  }

}

// Param is optional, to run task on UI thread.     

Handler handler = new Handler(Looper.getMainLooper());

Runnable runnable = new Runnable() {

    @Override

    public void run() {

        // Do the task...

        handler.postDelayed(this, milliseconds) // Optional, to repeat the task.

    }

};

handler.postDelayed(runnable, milliseconds);

// Stop a repeating task like this.

handler.removeCallbacks(runnable);

public class Address implements Cloneable

{

    public String street;

    public String city;

    public String state;

    public String zipCode;

}

final Query query = new Query(new Criteria().andOperator(

        Criteria.where(_id).is(id),

        Criteria.where(listA).elemMatch(Criteria.where(_id).is(id))

));

final Update update = new Update().addToSet(listA.$.listB, stuff).set(listA.$.thing, thing);

final WriteResult wr = mongoOperations.updateFirst(query, update, collectionName);

String str = abcdef;

char[] ch  = str.toCharArray();

for(char c : ch){

    int temp = (int)c;

    int temp_integer = 96; //for lower case

    if(temp<=122 & temp>=97)

        System.out.print(temp-temp_integer);

}

char inital = 'N';

// IT IS IMPORTANT TO REMEMBER TO USE SINGLE QUOTES WHEN WRITING CHAR OR IT WON'T WORK

static or class method

1) A method that is declared as static is known as the static method

2) We don't need to create the objects to call the static methods

3) Non-static (instance) members cannot be accessed in static context 

(static method, static block and static nested class) directly.

4) For example: public static int cube(int n){

return n*n*n*; (multiply *) }

Instance method

1) A method that is not declared as static is known as the instance method.

2) The object is required to call the instance method.

public class MyClass {

    static void myMethod() {

        System.out.println(You have called me! My name is: myMethod!);

    }

    public static void main(String[] args) {

        myMethod();

    }

}

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

/*in main*/

button.addActionListener(new ActionListener() {

  public void actionPerformed(ActionEvent e) {

            System.out.println('x');

  }

});

logging.level.org.springframework.security=DEBUG

String a = HYRE; 

String b = AGNYG;  

int compare = a.compareTo(b);  

if (compare < 0) {  

    //a is smaller

}

else if (compare > 0) {

    //a is larger 

}

else {  

    //a is equal to b

} 

Just some minor modification to your code will do (with some var renaming for clarity) :

double sum = 0; //average will have decimal point

for(int i=0; i < args.length; i++){

   //parse string to double, note that this might fail if you encounter a non-numeric string

   //Note that we could also do Integer.valueOf( args[i] ) but this is more flexible

   sum += Double.valueOf( args[i] ); 

}

double average = sum/args.length;

System.out.println(average );

Arrays.sort(myArr,(double[] a,double[] b)->{

                //here multiple lines of code can be placed

                return a[0]-b[0]; 

            });

car redCar = new Car(Red);

car Garage [] = new Car [100];

Garage[0] = redCar;

public static void main(String[] args) {

    double amount=0.0;

    try {

         amount = Double.parseDouble(txtMonth.getText());

    } catch (Exception e) {

        System.err.println(ups, this was not castable to double);

          amount=-10.0;

    }

    System.out.println(Here is the double: + amount);

}

int rand = ThreadLocalRandom.current().nextInt(x,y);

import android.util.Log;

Log.d(tagString, messageString);

// Using Kotlin

implementation(org.slf4j:slf4j-api:1.7.5)

implementation(org.slf4j:slf4j-log4j12:1.7.5)

@EnableWebMvc

@Configuration

@ComponentScan(com.baeldung.web)

public class WebConfig implements WebMvcConfigurer {

    // All web configuration will go here

}

int i=0;

while(i<10){

  if(i%2==0){

    i++;

    continue;// If it's pair we return to the while

  }

  System.out.println(i);// If is not we print it.

  i++;

}

// this keyword in java example

import java.util.*;

class Demo

{

   // instance variable

   int m;

   int n;

   public void setValue(int m, int n)

   {

      m = m;

      n = n;

   }

   public void showValue()

   {

      System.out.println(Value m =  + m);

      System.out.println(Value n =  + n);

   }

}

public class ThisKeywordDemo

{

   public static void main(String[] args)

   {

      Demo obj = new Demo();

      obj.setValue(5, 6);

      obj.showValue();

   }

}

public void iterateUsingIteratorAndEntry(Map<String, Integer> map) {

    Iterator<Map.Entry<String, Integer>> iterator = map.entrySet().iterator();

    while (iterator.hasNext()) {

        Map.Entry<String, Integer> entry = iterator.next();

        System.out.println(entry.getKey() + : + entry.getValue());

    }

}

char charValue = '2';

int intValue = Character.getNumericValue(charValue); // 2

public boolean isInteger(String numero){

    try{

        Integer.parseInt(numero);

        return true;

    }catch(NumberFormatException e){

        return false;

    }

}

Open up this file in your project:

<project>/gradle/wrapper/gradle-wrapper.properties

Edit the distributionUrl line and set it too:

distributionUrl=http\://services.gradle.org/distributions/gradle-1.8-all.zip

Rebuild your project.

</project>

  static boolean isPrime(int n){

        boolean result=true;

        if(n <= 1) return false;

        for(int i = 2; i <= n/2; i++){ //n/2 because the largest factor of any number is either it's half or less than it

            if(n % i == 0){

                result = false; //if some number divides it, then prime=false;

                break;

            }

        }

        return result;

    }

import java.util.Scanner;

public class Main {

    public static void main(String[] args) {

        // area of equilateral triangle

        Scanner scanner = new Scanner(System.in);

        System.out.print(Enter the equal length: );

        float equalLength = scanner.nextFloat();

        double area = (Math.sqrt(3) / 4) * Math.pow(equalLength,2);

        System.out.printf(The area is %.2f,area);

    }

}

Hash_table.containsKey(key_element)

import java.util.ArrayList;

import java.util.List;

public class ArrayListObjectToArrayMethodExample

{

   public static void main(String[] args)

   {

      List<Integer> al = new ArrayList<Integer>();

      al.add(12);

      al.add(14);

      al.add(16);

      al.add(18);

      al.add(20);

      Object[] obj = al.toArray();

      for(Object num : obj)

      {

         System.out.print(num +  );

      }

   }

}

 List<String> list = Arrays.asList(Lars, Simon);

public class StringExample 

{

    public static void main(String[] args) 

    {

        String blogName = howtodoinjava.com;

        blogName.startsWith(null);

    }

}

// Pascal triangle program in java without using arrays

import java.util.Scanner;

public class PascalTriangleDemo 

{

   public static void main(String[] args) 

   {

      System.out.println(Please enter number of rows to print pascal's triangle: );

      Scanner sc = new Scanner(System.in);

      int row = sc.nextInt();            

      System.out.println(Pascal's triangle with  + row +  rows.);

      displayPascalTriangle(row);

      sc.close();

   }

   public static void displayPascalTriangle(int r) 

   {

      for(int a = 0; a < r; a++) 

      {

         int num = 1;

         System.out.printf(% + (r - a) * 2 + s, ");

         for(int b = 0; b <= a; b++) 

         {

            System.out.printf(%4d, num);

            num = num * (a - b) / (b + 1);

         }

         System.out.println();

      }

   }

}

System.exit(n);

firstNum = numbers[0];

lastNum = numbers[numbers.length-1];

gcm -All java

//Clear example with good readabilty

String var = Text;

String shortHand = (var.equals(Text) ? Returns this if true : Returns this if false);

//Other example that is less readable

int var = 9;

int shortHand = var == 9 ? 1 : var++;

//Pseudo code

// CONDITION ? returns when true : returns when false

import java.awt.image.BufferedImage;

import java.awt.image.WritableRaster;

import java.io.File;

// w w w  . jav  a 2s  . com

import javax.imageio.ImageIO;

public class Main {

  public static void main(String[] args) throws Exception {

    BufferedImage img = colorImage(ImageIO.read(new File(NWvnS.png)));

    ImageIO.write(img, png, new File(Test.png));

  }

  private static BufferedImage colorImage(BufferedImage image) {

    int width = image.getWidth();

    int height = image.getHeight();

    WritableRaster raster = image.getRaster();

    for (int xx = 0; xx < width; xx++) {

      for (int yy = 0; yy < height; yy++) {

        int[] pixels = raster.getPixel(xx, yy, (int[]) null);

        pixels[0] = 0;

        pixels[1] = 255;

        pixels[2] = 255;

        raster.setPixel(xx, yy, pixels);

      }

    }

    return image;

  }

}

// matrix multiplication java

public class MatrixMultiplicationJavaDemo 

{

   public static int[][] multiplyMatrix(int[][] matrix1, int[][] matrix2, int row, int column, int col)

   {

      int[][] multiply = new int[row][col];

      for(int a = 0; a < row; a++) 

      {

         for(int b = 0; b < col; b++) 

         {

            for(int k = 0; k < column; k++) 

            {

               multiply[a][b] += matrix1[a][k] * matrix2[k][b];

            }

         }

      }

      return multiply;

   }

   public static void printMatrix(int[][] multiply) 

   {

      System.out.println(Multiplication of two matrices: );

      for(int[] row : multiply) 

      {

         for(int column : row) 

         {

            System.out.print(column +     );

         }

         System.out.println();

      }

   }

   public static void main(String[] args) 

   {

      int row = 2, col = 3;

      int column = 2;

      int[][] matrixOne = {{1, 2, 3}, {4, 5, 6}};

      int[][] matrixTwo = {{7, 8}, {9, 1}, {2, 3}};

      int[][] product = multiplyMatrix(matrixOne, matrixTwo, row, col, column);

      printMatrix(product);

   }

}

char ch=name.charAt(4);

//CodeHS AP Computer Science A Java, 9.2.7: Instruments

//DO NOT COPY AND PASTE, YOUR TEACHER CAN SEE YOUR EDIT HISTORY.

//Part 2/3

//Instrument.java

public class Instrument

{

    String name = ";

    String family = ";

    public Instrument(String name, String family){

        this.name = name;

        this.family = family;

    }

    public Instrument(String name){

        this.name = name;

    }

    public void setName(String str){

        this.name = str;

    }

    public String getName(){

        return this.name;

    }

    public void setFamily(String str){

        this.family = str;

    }

    public String getFamily(){

        return this.family;

    }

    public String toString(){

        return name +  is a member of the  + family +  family.;

    }

}

JLabel lab=new JLabel(text);

lab.setHorizontalAlignment(SwingConstants.LEFT);     

String[] myStringArray = new String[3];

String[] myStringArray = {a, b, c};

String[] myStringArray = new String[]{a, b, c};

import java.util.*; //or java.util.scanner

Scanner doit = new Scanner(System.in);//Name the scanner

System.out.println(Username:);//It will specify username

String username = doit.next();//Use scanner and add .next for string .nextInt for int and follows

//Get rows size matrix

matrix.length;

//Get columns size of matrix

matrix[0].length;

public class LinkedList {

    private Node head;

    private int length = 0;

    public LinkedList() {

        this.head = new Node(null);

    }

    public int size() {

        return length;

    }

     // Adds an element to the end of the list

    public void add(Object data)  {

        Node node = new Node(data);

        Node iterator = head;

        while (iterator.getNext() != null){

            iterator = iterator.getNext();

        }

        iterator.setNext(node);

        length++;

    }

     // Obtains an element by index

    public Object get(int index) {

        if (head.getNext() == null || index >= length){

            return null;

        }

        Node iterator = head.getNext();

        int counter = 0;

        while(counter < index){

            iterator = iterator.getNext();

            counter++;

        }

        return iterator.getData();

    }

     // Returns the index of the element in the list

    public int indexOf(Object data) {

        Node obj=head;

        for (int i = 0; i < length; i++) {

            obj = obj.getNext();

            if (obj.getData().equals(data)) {

                return i;

            }

        }

        return -1;

        //throw new Exception(Data not found);

    }

     // Removes an element from the list

    public boolean remove(Object data) {

        if (head.getNext() == null){

            return false;

        }

        Node iterator = head;

        while(iterator.getNext() != null){

            if (iterator.getNext().getData().equals(data)){

                iterator.setNext(iterator.getNext().getNext());

                length--;

                return true;

            }

            iterator = iterator.getNext();

        }

        return false;

    }

    private class Node {

        private Object data;

        private Node next;

        public Node(Object data) {

            this.data = data;

            next = null;

        }

        public Object getData() {

            return data;

        }

        public void setData(Object data) {

            this.data = data;

        }

        public Node getNext() {

            return next;

        }

        public void setNext(Node next) {

            this.next = next;

        }

    }

}

class DoublyLinkedList {    

    //A node class for doubly linked list

    class Node{  

        int item;  

        Node previous;  

        Node next;  

        public Node(int item) {  

            this.item = item;  

        }  

    }  

    //Initially, heade and tail is set to null

    Node head, tail = null;  

    //add a node to the list  

    public void addNode(int item) {  

        //Create a new node