InstanceOfJava

Type Casting in java?

Posted by: Instanceofjava Posted date: 12:13 PM / comment : 0 Java SE

Type Casting:

Type casting means to explicitly convert one type of data to another type of data.

Type casting has 2 types:

Upcasting
Downcasting

Upcasting:

Converting lower type value to upper type value is known as Upcasting.

http://instanceofjavaforus.blogspot.in/

Program:

package com.instanceofjavaforus;

public class Upcastingtest {

public static void main(String[] args) {

int a=100;

long b=a;

float c=b;

System.out.println(a);

System.out.println(b);

System.out.println(c);

}

Output:

100

100.0

Downcasting:

Converting upper type value to lower type value is known as Downcasting.

http://instanceofjavaforus.blogspot.in/

Program:

package com.instanceofjavaforus;

public class Downcastingtest {

public static void main(String[] args) {

double a=10.4;

long b=(long)a;

int c=(int)b;

System.out.println(a);

System.out.println(b);

System.out.println(c);

}

Output:

10.4

Program :

package com.instanceofjavaforus;
class Simple{
public static void main(String args[]){

char ch = 'A';
long a = ch;
System.out.println(a);
}

}

Output:
65

Program:

package com.instanceofjavaforus;
class Simple{
public static void main(String args[]) {
double d = 10.5;
int i = (int) d;
System.out.println(i);
}
}

Output:
10

Programming Interview Questions on loops

Posted by: Instanceofjava Posted date: 11:12 AM / comment : 11 Find Output of Program

Think Output:

Program #1:

package com.instanceofjavaforus;
public class Loops {
public static void main(String args[]){
int i=0;
for( i=0;i<5;i++){
System.out.println(i);
}
System.out.println("value of i after completion of loop: "+i);
}
}

Program #2:

package com.instanceofjavaforus;
public class LoopsDemo2 {
public static void main(String args[]){
int a=0,b=0;
for(int i=0;i<5;i++){
if(++a>2||++b>2){
a++;
}
}
System.out.println("a= "+a+" b="+b);
}
}

Program #3:

package com.instanceofjavaforus;
public class LoopsDemo3 {
public static void main(String args[]){
int i=5;
System.out.println(i++);
System.out.println(i--);
}
}

Convert Byte Array to String

Posted by: Instanceofjava Posted date: 9:01 AM / comment : 2 Core java Interview Questions , Java SE

To convert byte array to string we have a constructor in String class which is taking byte array as an argument.
So just we need to pass byte array object to string as argument while creating String class object.

package com.instanceofjavaforus;
public class ByteArrayToString {
/*
* This method converts a byte array to a String object.
*/
public static void convertByteArrayToString() {
byte[] byteArray = new byte[] {78,73, 67,69};
String value = new String(byteArray);
System.out.println(value);
}
public static void main(String[] args) {
ByteArrayToString.convertByteArrayToString();
}
}

Output:

NICE

Convert String to Byte Array:

package com.instanceofjava;
public class StringTOByteArray{
/*
* This example shows how to convert a String object to byte array.
*/
public static void main(String[] args) {
String data = "Instance of java";
byte[] byteData = data.getBytes();
System.out.println(byteData);
}
}

Output:

[B@3b26456a

Convert values of a Map to a List

Posted by: Instanceofjava Posted date: 10:47 PM / comment : 1 Collections , Java Programs

Java How To Convert Map Values To List In Java Some Different Ways Below are some common methods for doing so:

1. How to use values() with ArrayList

You can convert the values of a Map to a List in Java using various approaches.

below are a few common methods:

1. Using ArrayList andvalues()

import java.util.*;

public class MapToListExample {
    public static void main(String[] args) {
        Map<Integer, String> map = new HashMap<>();
        map.put(1, "Apple");
        map.put(2, "Banana");
        map.put(3, "Cherry");

        // Convert values to List
        List<String> list = new ArrayList<>(map.values());

        System.out.println(list);  // Output: [Apple, Banana, Cherry]
    }
}

2. Using Java 8 Stream API

import java.util.*;
import java.util.stream.Collectors;

public class MapToListExample {
    public static void main(String[] args) {
        Map<Integer, String> map = Map.of(1, "Apple", 2, "Banana", 3, "Cherry");

        // Convert values to List using Stream
        List<String> list = map.values().stream().collect(Collectors.toList());

        System.out.println(list);  // Output: [Apple, Banana, Cherry]
    }
}

3. Using forEach Loop

import java.util.*;

public class MapToListExample {
    public static void main(String[] args) {
        Map<Integer, String> map = new HashMap<>();
        map.put(1, "Apple");
        map.put(2, "Banana");
        map.put(3, "Cherry");

        List<String> list = new ArrayList<>();
        map.values().forEach(list::add);

        System.out.println(list);  // Output: [Apple, Banana, Cherry]
    }
}

💡 Choose the method based on your Java version:

Use ArrayList<>(map.values()) for simple cases.
Use Stream API (map.values().stream().collect(Collectors.toList())) in Java 8+ for a functional approach.
Use a forEach loop if modifying the list during iteration.

package com.instanceofjavaforus;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class MapValueToList {
Map<Integer, String> map;
public MapKeyToList(Map<Integer, String> map) {
this.map = map;
}
public List<String> convertValuesToList() {
return new ArrayList(map.values());
}
public static void main(String[] args) {
Map<Integer, String> map = new HashMap<>();
map.put(1, "one");
map.put(2, "two");
map.put(3, "three");
map.put(4, "Four");
map.put(5, "Five");
map.put(6, "Six");
map.put(7, "Seven");
map.put(8, "Eight");
map.put(9, "Nine");
map.put(10, "Ten");
MapValueToList conv = new MapValueToList (map);
List<String> keysList = conv.convertValuesToList();
System.out.println("Values:");
for (String val : keysList) {
System.out.println(val);
}
}
}
OutPut:
Values:
one
two
three
Four
Five
Six
Seven
Eight
Nine
Ten

Map to list in java example

Posted by: Instanceofjava Posted date: 10:09 PM / comment : 0 Collections

package com.instanceofjavaforus;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class MapKeyToList {
Map<Integer, String> map;
public MapKeyToList(Map<Integer, String> map) {
this.map = map;
}
public List<Integer> convertKeysToList() {
return new ArrayList(map.keySet());
}
public static void main(String[] args) {
Map<Integer, String> map = new HashMap<>();
map.put(1, "one");
map.put(2, "two");
map.put(3, "three");
map.put(4, "Four");
map.put(5, "Five");
map.put(6, "Six");
map.put(7, "Seven");
map.put(9, "Nine");
map.put(10, "Ten");
MapKeyToList conv = new MapKeyToList(map);
List<Integer> keysList = conv.convertKeysToList();
System.out.println("Keys:");
for (Integer key : keysList) {
System.out.println(key);
}
}
}
OutPut:
Keys:
1
2
3
4
5
6
7
8
9
10

Marker Interfaces in java

Posted by: Instanceofjava Posted date: 3:51 PM / comment : 0 Java SE

Marker interface:

The interfaces using which we explicitly mention or mark certain properties to the object are known as marker interface.
An interface that is used to check / mark / tag the given object is of a specific type to perform a special operations on that object.
Marker interfaces will not have methods , they are empty interfaces.

Need of marker interface:

It i used to check , whether we can perform some special operations on the passed object
For ex: using serializable interface we can explicitly mention that object of a class is transferable. else it can not.
If a class is deriving form java.lang.Cloneable interface then that object can be cloned, else it can not
In side those particular methods , that method developer will check that the passed object is of type the given interface or not by using "instanceof" operator.

Predefined marker interfaces:

java.lang.Cloneable
java.io.Serializable
java.util.RandomAccess
java.util.Eventlistener
java.rmi.Remote
java.servlet.SingleThreadModel

Subscribe to: Posts ( Atom )