InstanceOfJava

How to Convert string to StringBuilder and vise versa in Java

Posted by: Instanceofjava Posted date: 10:45 AM / comment : 0 java programming interview questions

We can Covert String to string builder in two ways

Using constructor of StringBuilder(String s)
Using append method of StringBuilder

Lets see a java program to convert java String object to StringBuilder using constructor of StringBuilder class.

#1: Java program to convert string to StringBuilder using constructor of StringBuilder class.

package com.instanceofjava;
/**
* @author www.Instanceofjava.com
* @category interview programs
*
* Description: Java Program to convert String to StringBuilder
*
*/
public class StringBuilderDemo {
public static void main(String[] args) {
String str="java";
StringBuilder sb = new StringBuilder(str);
String s = sb.toString();
System.out.println(s);
StringBuilder stebldr= new StringBuilder("convert string to stringbuilder");
String st = stebldr.toString();
System.out.println(st);
}
}

Output

java
convert string to stringbuilder

#2: Java program to convert string to StringBuilder using append method of StringBuilder class.

package com.instanceofjava;
/**
* @author www.Instanceofjava.com
* @category interview programs
*
* Description: Java Program to convert String to StringBuilder
*
*/
public class StringBuilderDemo {
public static void main(String[] args) {
StringBuilder sb = new StringBuilder();
sb.append("Java convert string to StringBuilder ");
System.out.println(sb);
String str= "Convert string to Stringbuilder" ;
sb.append(str);
System.out.println(sb);
}
}

Output

Java convert string to StringBuilder
Java convert string to StringBuilder Convert string to Stringbuilder

We can Convert StringBuilder to String by using toString() method of StringBuilder class.
How to convert StringBuilder to String in java.

#3: Java program to convert string to StringBuilder using append method of StringBuilder class.

package com.instanceofjava;
/**
* @author www.Instanceofjava.com
* @category interview programs
*
* Description: Java Program to convert StringBuilder to String
*
*/
public class StringBuilderDemo {
public static void main(String[] args) {
StringBuilder sb = new StringBuilder();
sb.append("Java convert StringBuilder to string");
String str=sb.toString();
System.out.println(str);
String s= "Convert Stringbuilder to string " ;
sb.append(s);
String st=sb.toString();
System.out.println(st);
}
}

Output

Java convert StringBuilder to string
Java convert StringBuilder to stringConvert Stringbuilder to string

java program to convert string to string builder

Java Program to check a String is palindrome or not by ignoring its case

Posted by: Instanceofjava Posted date: 3:32 PM / comment : 0 java programming interview questions , java programs for freshers

A palindrome is a word that reads the same backward or forward.
Lets see what if the characters in a palindrome string are in different case. i.e should not be case sensitive.
So now we will see how to check a string is palindrome or not by ignoring its case.
Write a function which checks that string is palindrome or not by converting the original string to lowercase or uppercase.
Method should return true if it is palindrome, return false if not a palindrome.

#1 : Java Program to check given string is palindrome or not by ignoring its case.

package com.instanceofjava;
public class CheckPalindrome {
public static boolean isPalindrome(String str) {
StringBuffer strone=new StringBuffer(str.toLowerCase());
StringBuffer strtwo=new StringBuffer(strone);
strone.reverse();
System.out.println("Orginal String ="+strtwo);
System.out.println("After Reverse ="+strone);
if(String.valueOf(strone).compareTo(String.valueOf(strtwo))==0)
return true;
else
return false;
}
public static void main(String[] args) {
boolean ispalindrome= isPalindrome("DeleveleD");
System.out.println(ispalindrome);
}
}

Output

Orginal String =deleveled
After Reverse =deleveled
true

check palindrome or not ignore case sensitive

How to Delete folder and subfolders using Java 8

Posted by: Instanceofjava Posted date: 11:29 PM / comment : 0 java programming interview questions

How to delete folder with all files and sub folders in it using java 8.
We can use java 8 Stream to delete folder recursively
Files.walk(rootPath, FileVisitOption.FOLLOW_LINKS)
.sorted(Comparator.reverseOrder())
.map(Path::toFile)
.peek(System.out::println)
.forEach(File::delete);

Files.walk - this method return all files/directories below the parent folder
.sorted - sort the list in reverse order, so the folder itself comes after the including subfolders and files
.map - map the file path to file
.peek - points to processed entry
.forEach - on every File object calls the .delete() method

#1: Java Example program to delete folders and subfolders using java 8 stream

package com.instanceofjava;
import java.io.File;
import java.io.IOException;
import java.nio.file.FileVisitOption;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.Comparator;
/**
* @author www.Instanceofjava.com
* @category interview questions
*
* Description: delete folders and sub folders using java 8
*
*/
public class DeleteFolder {
public static void main(String[] args) {
Path rootPath = Paths.get("C:\\Users\\Saidesh kilaru\\Desktop\\folder1");
try {
Files.walk(rootPath, FileVisitOption.FOLLOW_LINKS)
.sorted(Comparator.reverseOrder())
.map(Path::toFile)
.peek(System.out::println)
.forEach(File::delete);
} catch (IOException e) {
e.printStackTrace();
}
}
}

Output:

C:\Users\Saidesh kilaru\Desktop\folder1\subfolder\file2 in sub folder.docx
C:\Users\Saidesh kilaru\Desktop\folder1\subfolder
C:\Users\Saidesh kilaru\Desktop\folder1\file1.docx
C:\Users\Saidesh kilaru\Desktop\folder1

How to Convert integer set to int array using Java 8

Posted by: Instanceofjava Posted date: 11:26 PM / comment : 0 java programming interview questions

How to convert Integer Set to primitive int array.
By Using java 8 Streams we can convert Set to array.
set.stream().mapToInt(Number::intValue).toArray();
Lets see an example java program on how to convert integer set to int array using java 8

#1: Java Example program on converting Integer Set to int Array

package com.instanceofjava;
import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
public class SetToArray {
/**
* @author www.Instanceofjava.com
* @category interview programming questions
*
* Description: convert Integer set to int array using java 8
*
*/
public static void main(String[] args) {
Set<Integer> hashset= new HashSet<>(Arrays.asList(12,34,56,78,99));
int[] array = hashset.stream().mapToInt(Number::intValue).toArray();
for (int i : array) {
System.out.println(i);
}
}
}

Output:

In Java, a Set is a collection that contains no duplicate elements and is unordered. To convert a Set to an array, you can use the toArray() method of the Set interface. This method returns an array containing all of the elements in the Set in the order they are returned by the iterator.

Set<Integer> set = new HashSet<>();

set.add(1);

set.add(2);

set.add(3);

Integer[] array = set.toArray(new Integer[set.size()]);

In this example, we first create a HashSet of integers, add some elements to it, then we use the toArray method to convert it to an array of integers.

toArray(T[] a) method where we can pass an empty array of a specific type, the method will fill the array with the elements from the set, this is useful if you know the size of the array that you need.

converting a Set to an array in Java can be done using the toArray() method of the Set interface. The method returns an array containing all of the elements in the Set in the order they are returned by the iterator. This method can also accept an empty array of a specific type, the method will fill the array with the elements from the set.

Initializing a boolean array in java with an example program

Posted by: Instanceofjava Posted date: 9:27 PM / comment : 0 arrays , java programming interview questions

Initializing a boolean variable : boolean b=true;
In some cases we need to initialize all values of boolean array with true or false.
In such cases we can use Arrays.fill() method
Arrays.fill(array, Boolean.FALSE);
java initialize boolean array with true: Arrays.fill(array, Boolean.FALSE);
Lets see an example java program on how to assign or initialize boolean array with false or true values.

#1: Java Example program on initializing boolean array.

package com.instanceofjava;
import java.util.Arrays;
/**
* @author www.Instanceofjava.com
* @category interview questions
*
* Description: Initialize boolean array values with false or true
*
*/
public class InitializeBoolean {
public static void main(String[] args) {
Boolean[] array = new Boolean[4];
//initially all values will be null
for (int i = 0; i < array.length; i++) {
System.out.println(array[i]);
}
Arrays.fill(array, Boolean.FALSE);
// all values will be false
for (int i = 0; i < array.length; i++) {
System.out.println(array[i]);
}
Arrays.fill(array, Boolean.TRUE);
// all values will be false
for (int i = 0; i < array.length; i++) {
System.out.println(array[i]);
}
}
}

Output:

null
null
null
null
false
false
false
false
true
true
true
true

Java 8 initialize set with values with an example program

Posted by: Instanceofjava Posted date: 9:05 PM / comment : 0 java programming interview questions , java8

We can initialize set while defining by passing values to constructor.
For example to initialize HashSet we can use Arrays.asList(value1,value2).
Set<Integer> hashset = new HashSet<>(Arrays.asList(12, 13));

#1: Java Example program to initialize set without using java 8

import java.util.Arrays;
import java.util.HashSet;
import java.util.Set;
/**
* @author www.Instanceofjava.com
* @category interview questions
*
* Description: Initialize set
*
*/
public class InitializeSet {
public static void main(String[] args) {
Set<Integer> hashset = new HashSet<>(Arrays.asList(12, 13));
System.out.println(hashset);
}
}

Output:

[12, 13]

We can initialize set in java 8 using Stream.
Stream.of("initialize", "set").collect(Collectors.toSet());

#2: Java Example program to initialize set without using java 8

import java.util.Set;
import java.util.stream.Collectors;
import java.util.stream.Stream;
/**
* @author www.Instanceofjava.com
* @category interview questions
*
* Description: Initialize set using java 8 Stream
*
*/
public class InitializeSet {
public static void main(String[] args) {
Set<String> set = Stream.of("initialize", "set").collect(Collectors.toSet());
System.out.println(set);
}
}

Output:

[set, initialize]

We can initialize Set in java 8 by creating stream from an Array and list

#3: Java Example program to initialize set without using java 8

java 8 initialize set with values with an example program

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