{public | private} [static] type name [= expression | value];

{public | private} [static] {type | void} name(arg1, ..., argN ){statements}

 // Widening (byte<short<int<long<float<double)
int i = 10; //int-->; long
long l = i; //automatic type conversion
// Narrowing
double d = 10.02;
long l = (long)d; //explicit type casting
// Numeric values to String
String str = String.valueOf(value);
// String to Numeric values
int i = Integer.parseInt(str)
double d = Double.parseDouble(str);

/ Using BufferReader
BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
String name = reader.readLine();
// Using Scanner
Scanner in = new Scanner(System.in);
String s = in.nextLine();
int a = in.nextInt();
// Using Console
String name = System.console().readLine();

public class Demo{
   public static void main(String[] args){
      System.out.println("Hello from edureka!");
   }
}

You need to save your Java Program by the name of the class containing main() method along with .java extension.

className.java

Call the compiler using javac command.

javac className

Finally, execute the program using below code:

java className

// for loop
for (condition) {expression}
// for each loop
for (int i: someArray) {}
// while loop
while (condition) {expression}
// do while loop
do {expression} while(condition)

Generating a Fibonacci series.

for (i = 1; i <= n; ++i){
   System.out.print(t1 + " + ");
   int sum = t1 + t2;
   t1 = t2;
   t2 = sum;
}

Creating a pyramid pattern.

k = 2*n - 2;
for(i=0; i<n; i++){
   for(j=0; j<k; j++){System.out.print(" ");}
   k = k - 1;
   for(j=0; j<=i; j++ ){System.out.print("* ");}
   System.out.println();
}

//if statement
if (condition) {expression}
//if-else statement
if (condition) {expression} else {expression}
//switch statement
switch (var)
{ case 1: expression; break; default: expression;  break; }

Checking the given number is prime or not.

if (n < 2) { return false; }
for (int i=2; i <= n/i; i++)
{if (n%i == 0) return false;}
return true;

Finding the factorial using recursion function.

int factorial(int n)
  {
   if (n == 0)
     {return 1;}
   else
     {return(n * factorial(n-1));}
 }

// Initializing
type[] varName= new type[size];
// Declaring
type[] varName= new type[]{values1, value2,...};

Creating an array with random values.

double[] arr = new double[n];
for (int i=0; i<n; i++){
 a[i] = Math.random();
}

Searching the max value in the array.

double max = 0;
for(int i=0; i<arr.length(); i++){
 if(a[i] > max) max = a[i];
}

Reversing an array.

for(int i=0; i<(arr.length())/2; i++){
 double temp = a[i];
 a[i] = a[n-1-i];
 a[n-1-i] = temp;
 }

// Initializing
datatype[][] varName  =  new dataType[row][col];

// Declaring
datatype[][] varName  =  {{value1, value2....},{value1, value2....}..};

Transposing a matrix.

for(i = 0; i < row; i++){
for(j = 0; j < column; j++)
    { System.out.print(array[i][j]+" "); }
    System.out.println(" ");
}

Multiplying two matrices.

for (i = 0; i < row1; i++){
   for (j = 0; j < col2; j++){
      for (k = 0; k < row2; k++){
         sum = sum + first[i][k]*second[k][j];
      }
      multiply[i][j] = sum;
      sum = 0;
    }
}

String str1 = “Welcome”; // Using literal

String str2 = new String(”Edureka”); // Using new keyword

str1 == str2 //compares address;
String newStr = str1.equals(str2); //compares the values
String newStr = str1.equalsIgnoreCase() //compares the values ignoring the case
newStr = str1.length() //calculates length
newStr = str1.charAt(i) //extract i'th character
newStr = str1.toUpperCase() //returns string in ALL CAPS
newStr = str1.toLowerCase() //returns string in ALL LOWERvCASE
newStr = str1.replace(oldVal, newVal) //search and replace
newStr = str1.trim() //trims surrounding whitespace
newStr = str1.contains("value"); //check for the values
newStr = str1.toCharArray(); // convert String to character type array
newStr = str1.IsEmpty(); //Check for empty String
newStr = str1.endsWith(); //Checks if string ends with the given suffix