1. Sieve public class sieve { public static void main(String args[]) {
int max = 100;
boolean prime[] = new boolean[max+1];
int n,m;
// initialize the array (entries 0,1 unused)
for (n = 2; n <= max; n++) {
prime[n] = true; }
// cross out multiples of uncrossed numbers
if (prime[n]) {
for (m = 2*n; m <= max; m += n)
prime[m] = false;
// print out primes: uncrossed numbers
System.out.print(n+" ");
System.out.println();

2. Queue
class Queue {
char q[]; // this array holds the queue
int putloc, getloc; // the put and get indices
Queue(int size) {
q = new char[size+1]; // allocate memory for queue
putloc = getloc = 0; }
boolean isEmpty(){
if (getloc == putloc) return true;
else return false;
boolean isFull(){
if (putloc == q.length-1) return true;

3. // put a characer into the queue
void put(char ch) {
if (isFull()) {
System.out.println(" -- Queue is full.");
return; }
putloc++;
q[putloc] = ch;
// get a character from the queue
char get() {
if (isEmpty()){
System.out.println(" -- Queue is empty.");
return (char) 0;
getloc++;
return q[getloc];

4. // Demonstrate the Queue class.
class QueueDemo {
public static void main(String args[]) {
Queue bigQ = new Queue(100);
Queue smallQ = new Queue(4);
char ch;
int i;
System.out.println("Using bigQ to store the alphabet.");
// put some numbers into bigQ
for(i=0; i < 26; i++)
bigQ.put((char) ('A' + i));
// retrieve and display elements from bigQ
System.out.print("Contents of bigQ: ");
for(i=0; i < 26; i++) {
ch = bigQ.get();
if(ch != (char) 0) System.out.print(ch); }
System.out.println("\n");

5. System.out.println("Using smallQ to generate erros.");
// Now, use smallQ to generate some errors
for(i=0; i < 5; i++) {
System.out.print("Attempting to store " +
(char) ('Z' - i));
smallQ.put((char) ('Z' - i));
System.out.println(); }
// more errors on smallQ
System.out.print("Contents of smallQ: ");
ch = smallQ.get();
if(ch != (char) 0) System.out.print(ch);

6. Stack
class Stack {
int st[]; // this array holds the stack
int sp; // the stack pointer index
Stack(int size) {
st = new int[size+1]; // allocate memory for stack
sp = 0; }
boolean isFull(){
if (sp == (st.length-1)) return true;
else return false;
boolean isEmpty(){
if (sp == 0) return true;

7. void push(int n) {
if(isFull()) {
System.out.println(" -- Stack is full.");
return; }
sp++;
st[sp] = n;
int pop() {
int top;
if(isEmpty()) {
System.out.println(" -- Stack is empty.");
return -1000;
top = st[sp];
sp--;
return top;

8. // Demonstrate the Stack class.
class StackDemo {
public static void main(String args[]) {
Stack st1 = new Stack(5);
int i,n;
System.out.println("Using stack st1 to store numbers.");
// put some numbers into st1
for(i=1; i < 7; i++)
st1.push(i);
// pop and display elements from st1
System.out.println("Contents of st1: ");
for(i=1; i < 7; i++) {
n = st1.pop();
if (n != -1000) System.out.println(n); }