Hi Friend,

1)Following code displays the prime numbers between 1 to 20.

class PrimeNumbers{
public static void main (String args[]){
String primeNo = "";
int j=0;
System.out.println("Prime Numbers are:" );
for (int i = 1; i < 20; i++){ {
for ( j = 2; j < i; j++){
if (i % j == 0) {
break;
}
}
if (i == j) {
primeNo += i + " ";
}
}
}
System.out.println(primeNo);
}
}

2) Following code displays Even and Odd numbers between 1 to 20.

class EvenAndOddNumbers{
public static void main (String args[]){
String evenNo = "";
String oddNo = "";
for (int i = 1; i <=20; i++){
if (i % 2 == 0) {
evenNo += i + " ";
}
else{
oddNo +=i+ " ";
}
}
System.out.println("Even Numbers between 1 to 20 are: "+evenNo);
System.out.println("Odd Numbers between 1 to 20 are: "+oddNo);
}
}

Hope that it will be helpful for you.

Thanks