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Input Output in Java
import java.util.Scanner; // Import the Scanner class
class Main {
public static void main(String[] args) {
Scanner myObj = new Scanner(System.in);
System.out.println("Enter name, age and salary:");
// String input
String name = myObj.nextLine();
// Numerical input
int age = myObj.nextInt();
double salary = myObj.nextDouble();
// Output input by user
System.out.println("Name: " + name);
System.out.println("Age: " + age);
System.out.println("Salary: " + salary);
}
}
Method Description
nextBoolean() Reads a boolean value from the user
nextByte() Reads a byte value from the user
nextDouble() Reads a double value from the user
nextFloat() Reads a float value from the user
nextInt() Reads a int value from the user
nextLine() Reads a String value from the user
nextLong() Reads a long value from the user
nextShort() Reads a short value from the user
When we don't know number of input
// Check if an int value is available
while (sc.hasNextInt())
{
// Read an int value
int num = sc.nextInt();
sum += num;
count++;
}
if else
if (time < 18) {
System.out.println("Good day.");
} else {
System.out.println("Good evening.");
}
Switch
switch(expression) {
case x:
// code block
break;
case y:
// code block
break;
default:
// code block
}
While loop
int i = 0;
while (i < 5) {
System.out.println(i);
i++;
}
Do-While loop
int i = 0;
do {
System.out.println(i);
i++;
}
while (i < 5);
Break
for (int i = 0; i < 10; i++) {
if (i == 4) {
break;
}
System.out.println(i);
}
Continue
for (int i = 0; i < 10; i++) {
if (i == 4) {
continue;
}
System.out.println(i);
}
Array
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
for (int i = 0; i < cars.length; i++) {
System.out.println(cars[i]);
}
2nd Way Array (When value don't know)
int intArray[]; //declaring array
intArray = new int[20]; // allocating memory to array
OR
int[] intArray = new int[20]; // combining both statements in one
note-The elements in the array allocated by new will automatically be initialized to zero (for numeric types), false (for boolean), or null
(for reference types).
for - each loop
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
for (String i : cars) {
System.out.println(i);
}
Class in Java
class Student{ public int roll_no; public String name; Student(int roll_no, String name) { this.roll_no = roll_no; this.name = name; }}
Multidimensional Array
int[][] intArray = new int[10][20]; //a 2D array or matrix
int[][][] intArray = new int[10][20][10]; //a 3D array
Passing Array in Function
class Main
{
// Driver method
public static void main(String args[])
{
int arr[] = {3, 1, 2, 5, 4};
// passing array to method m1
avg(arr);
}
public static void avg(int[] arr)
{
// getting sum of array values
int av = 0;
for (int i = 0; i < arr.length; i++)
av+=arr[i];
System.out.println("sum of array values : " + av/arr.length);
}
}
Returning Arrays from Methods
class Test
{
// Driver method
public static void main(String args[])
{
int arr[] = m1();
for (int i = 0; i < arr.length; i++)
System.out.print(arr[i]+" ");
}
public static int[] m1()
{
// returning array
return new int[]{1,2,3};
}
}
Cloning of array(Deep Copy)
class Test
{
public static void main(String args[])
{
int intArray[] = {1,2,3};
int cloneArray[] = intArray.clone();
// will print false as deep copy is created
// for one-dimensional array
System.out.println(intArray == cloneArray);
for (int i = 0; i < cloneArray.length; i++) {
System.out.print(cloneArray[i]+" ");
}
}
}
Output:
false1 2 3
Inbuilt List
// Java program to demonstrate a List
import java.util.*;
public class ListDemo { public static void main(String[] args) { // Creating a list List<Integer> l1 = new ArrayList<Integer>();
// Adds 1 at 0 index l1.add(0, 1);
// Adds 2 at 1 index l1.add(1, 2); System.out.println(l1);
// Creating another list List<Integer> l2 = new ArrayList<Integer>();
l2.add(1); l2.add(2); l2.add(3);
// Will add list l2 from 1 index l1.addAll(1, l2); System.out.println(l1);
// Removes element from index 1 l1.remove(1); System.out.println(l1);
// Prints element at index 3 System.out.println(l1.get(3));
// Replace 0th element with 5 l1.set(0, 5); System.out.println(l1); //Sorting the list
//Creating a list of fruits List<String> list1=new ArrayList<String>(); list1.add("Mango"); list1.add("Apple"); list1.add("Banana"); list1.add("Grapes"); //Sorting the list Collections.sort(list1);
// Remove via object
list1.remove("Banana"); System.out.println("After the Object Removal " + list1);
// Iterating the list
// for loop for (int i = 0; i < list1.size(); i++) { System.out.print(list1.get(i) + " "); } System.out.println(); // Using the for each loop for (String str : list1) System.out.print(str + " ");
}}
Output[1, 2][1, 1, 2, 3, 2][1, 2, 3, 2]2[5, 2, 3, 2][2, 2, 3, 5]
[Apple, Banana, Grapes, Mango]
After the Object Removal [Apple, Grapes, Mango]
Apple Grapes Mango Apple Grapes Mango
String
String LiteralString Literal memory Allocates in String constant poolString str = "Geeks";
Create String using new operatorString str = new String("Geeks");If you want to store this string in the constant pool then you will need to “intern” it.
For example:
String internedString = str.intern(); // this will add the string to string constant pool.
public class StringExample{ public static void main(String args[]){ String s1="java";//creating string by java string literal char ch[]={'s','t','r','i','n','g','s'}; String s2=new String(ch);//converting char array to string String s3=new String("example");//creating java string by new keyword System.out.println(s1); System.out.println(s2); System.out.println(s3);
String str="python"; System.out.println("string length is: "+str.length());
}} }}
Outputjava
strings
example string length is: 6
StringBufferStringBuffer s = new StringBuffer("GeeksforGeeks");
StringBuilderStringBuilder str = new StringBuilder();str.append("GFG");
int to Integer conversion
public class IntToInteger{ public static void main(String[] args) { int i = 78; Integer obj = new Integer(i); System.out.println(obj); }}
output= 78
Integer to int conversion
import java.lang.*;
public class IntgerToInt {
public static void main(String[] args) {
Integer posobject = new Integer(88);
// Returns the value of this Integer as an int int i = posobject.intValue(); System.out.println("The integer Value of i = " + i);
Integer negobject = new Integer(-89); // Returns the value of this Integer as an int int i2= negobject.intValue(); System.out.println("The integer Value of i2 = " + i2);
}}
output= The integer Value of i = 88
The integer Value of i = -89
Inheritance
Inheritance is used to achieve runtime polymorphism.
PolymorphismIf one task is performed in different ways, it is known as polymorphism.
Static Block and Static method First, JVM executes the static block, then it executes static methods, and then it creates the object needed by the program. Finally, it executes the instance methods. class Demo { static //static block { System.out.println("Static block"); } public static void main(String args[]) //static method { System.out.println("Static method"); } } Output:
Static blockStatic method
A program that does not have the main() method gives an error at run time.
class DemoStaticBlock { Static //static block { System.out.println("Static block"); } } Output:
Error: Main method not found in the class Demo, please define the main method as:public static void main(String[] args)or a JavaFX application class must extend javafx.application.Application
Method Overriding-Static method can not override because It is related to class and gets memory to class area.
Access modifiersClass can not private or protected instead of nested class.
If you are overriding any method, overridden method (i.e. declared in subclass) must not be more restrictive.
Calling orderParent Class constrctor ->Instance Intializer Block ->constructor -> Method
Final-If final Variable is not Intialize then it is known as blank final variable. It is intialise only in constructor.If static final Variable is not Intialize then it is known as static blank final variable. It is intialise only in static block.
Final class can not extended (Hence Inheritance does not apply in final class).
final parameter can not change its value.
Upcasting-If the reference variable of Parent class refers to the object of Child class, it is known as upcasting.
Compile Time Polymorphism-Overloading of static method
Runtime Poly-Reference of parent class point child class object calls overidden method of child class is decide at run time.Runtime polymorphism can't be achieved by data members.
Binding-Connecting a method call to the method body is known as binding.
Static Binding -Type of object determined at comile timeIf there is any private, final or static method in a class, there is static binding.
Dynamic Binding -Type of object determined at run time
Object have a typeAn object is an instance of particular java class,but it is also an instance of its superclass.
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