Thread: Page Replacement Algorithms

here is the code i've assembled so far... I am having some errors compiling it but I believe it is executing the FIFO method. Any suggestions to why my code isn't working ?

/* explaining how to capture user input via the console
At the top of the program "import java.util.Scanner;"
 
in the main thread (public static void main())
 
you can do something like ->
 
	Scanner in = new Scanner(System.in);
	System.out.println("Input pages :");
	int pages = in.nextInt();
 
	System.out.println("Input frames :");
	int frames = in.nextInt();
 
	System.out.println("Input process run time :");
	int runtime = in.nextInt();
 
	in.close(); 	//to avoid extra memory and so on ;)
 
 
Now you got the 3 variables needed instead of hardcoding them later on //you can make checks on each of the inputs to make sure they meet the standard (ie, they're in the correct range) before committing it to a variable
*/
 
 
---------------------------------------->
 
 
 
class Page {
private boolean isInMemory = false;
private int pageNumber;
 
	public Page(int number) {pageNumber = number;}
 
	public void setActive() {isInMemory = true; }
	public boolean getActive() {return isInMemory; }
}
 
 
---------------------------------------->
 
class Memory {
private Page page = null;
 
	public Memory(Page p) {page = p;}
 
	public Page getPage() {return page; }
}
 
 
---------------------------------------->
 
 
public static void main(String[] args) {
 
	Scanner in = new Scanner(System.in);
	System.out.println("Input pages :");
	int pagesIn = in.nextInt();
 
	System.out.println("Input frames :");
	int framesIn = in.nextInt();
 
	System.out.println("Input process run time :");
	int runtimeIn = in.nextInt();
 
	in.close(); 	//to avoid extra memory and so on ;)
 
 
 
	int pages = pages; ;
	int memory = framesIn;
	int pageReferences = runtimeIn;		//process
 
	Page[] pageTable = new page[pages];
 
	for(int i = 0; i<pages; i++) {
		pageTable[i] = new Page(int i);
	}	
 
	ArrayList<Memory> memList = new ArrayList<Memory>();
	ArrayList<Page> pageList = new ArrayList<Page>();
 
	for(int i = 0; i<pageReferences; i++) {
		int pageIndex = Math.rand()*pages;	//make a random number between 1 and 20 (the number of pages)
		Page p = pageTable[pageIndex];
		pageList.add(p);
	}
 
 
---------------------------------------->
 
	int pageFaultCount = 0;
	for(Page p : pageList) {I'
			if(!p.getActive) {
				p.setActive();
			}
 
			if(memList.size() < memory) {
				memList.add(p);
			} else {
				memList.remove(0);
				memList.add(0,p);	//add 'p' to the list at the first position in the list (index = 0)
				pageFaultCount++;
			}
		}
	}
}
 
	//After this you can write out the pageFaultCount for statistics
	//Since this is just one "algorithm" I've made out from the document, there should be 3 algorithms to implement. And write the stats for those 3
 
	//(FIFO – First In First Out, LRU – Least Recently Used, and the Clock).
	//The one I made was a FIFO, LRU should be almost exactly the same as FIFO, just instead of adding at index = 0, then add it at the highest index
	//I don't know what the Clock method is

FIFO is best implemented as a Queue (and indirectly, a linked list). For the Least Recently Used, I think you might be able to implement that as a Priority Queue (through a heap), just keep track of when the page was last used.

Wikipedia: Queue Data Structure
Wikipedia: Heap Data Structure

If you can, just use Java's Queue and Priority Queue classes.