Loop is used to execute a statement or some statements multiple times. There are 3 types of loop control in java.

1. For Loop
2. While Loop
3. Do While Loop

For Loop

For loop pattern:

for(initialization;condition;increment){
    //statement
}

A simple program in for loop:

1. Write a program to show only odd numbers from 1 to 100

public class Main {
    public static void main(String[] args) {
        for(int i=1;i<=100;i++){
            if(i%2!=0){
                System.out.println(i);
            }
        }
    }
}

2. Write a program to show first 100 prime numbers:

public class Main {
    public static void main(String[] args) {

        String  primeNumbers = "";

        for (int i = 1; i <= 100; i++)
        {
            int counter=0;
            for(int num =1; num<=i; num++)
            {
                if(i%num==0)
                {
                    counter = counter + 1;
                }
            }
            if (counter ==2)
            {
                primeNumbers = primeNumbers + i + " ";
            }
        }
        System.out.println("Prime numbers from 1 to 100 are :");
        System.out.println(primeNumbers);

    }

} 

while(condition) {
  //statement;
}
or
initialization;
while(condition) {
//statement;
increment;
}

A simple program in while loop:

1. Write a program to find out factorial of a number.

public class Main {
    public static void main(String[] args) {
        int number=5;
        int i=1;
        int fact=1;
        while(i <=number){
            fact=fact*i;
            i++;
        }
        System.out.println(fact);

    }

}

Output: 120

2. Write a program to find the summation of digits.

public class Main {
    public static void main(String[] args) {
        int sum = 0;
        Scanner s = new Scanner(System.in);
        System.out.print("Enter a number:");
        int num = s.nextInt();
        while(num != 0)
        {
            int res = num % 10;
            sum = sum + res;
            num = num / 10;
        }

        System.out.println("Sum of Digits:"+sum);

    }

}

Output:
Enter a number:1241
Sum of Digits:8

Do While Loop

While loop and do while loop are same just a pretty much difference that is, while loop check the condition at first and do while check the condition after executing the statement.

Pattern:

do {
  // code block to be executed
}
while (condition);

A simple program in do-while loop:

1. Write a program to find factorial of a number.

public static void main(String[] args) {
    int number=5;
    int i=1;
    int fact=1;
    do{
        fact=fact*i;
        i++;
    }
    while(i <=number);
    System.out.println(fact);

}

Output: 120