i got the following class for the queue.
public class queueArray {
final int maxNumbers=1000;
protected Item[] arrayInfo;
protected int head ,tail;
public queueArray(){
head=tail=0;
arrayInfo= new Item[maxNumbers];
}
public boolean isEmpty(){
return(head==tail && arrayInfo[tail]==null);
}
public void insert(Item a){
if(head == tail && arrayInfo[tail]!=null){
System.out.println("Η ουρά είναι γεμάτη.");
return;
}
arrayInfo[tail]=a;
tail=(tail+1)%maxNumbers;
}
public Item removeFirst(){
if (head == tail && arrayInfo[head]!=null){
System.out.println("Η ουρά είναι γεμάτη.");
return null;
}
arrayInfo[head]=null;
head=(head+1)%maxNumbers;
return arrayInfo[head];
}
}
How can i made an extra method that reverses queue's clues?
If you use the .NET Queue class, then you can just call Reverse() for example:
Queue<int> q = new Queue<int>();
q.Enqueue(1);
q.Enqueue(2);
q.Enqueue(15);
q.Enqueue(22);
q.Reverse();
One way of doing this would be to pull all of the elements from the front of the queue and push them to a stack. Then pull from the top of the stack and push those elements back to the queue.
Related
Something that has been bothering me for a long time is why do the following lines of code have the same results.
Code 1:
Transform[] childs = gameObject.GetComponentsInChildren<Transform>();
foreach(Transform child in childs) { Debug.Log(child.name); }
Code 2:
foreach(Transform child in gameObject.transform) { Debug.Log(child.name); }
This is actuallly a pseudo-code, I didn't really test it but should be enough to explain.
My question is, what's happening on Code 2 ? Is gameObject.transform actually an array of Transform ? Why doesn't Code 2 print the name of the parent gameObject ?
Maybe this is something very simple and obvious I'm just overlooking but I can't make it out right now.
Transform implements the IEnumerable interface. This interface is what allows the use of the foreach keyword.
public partial class Transform : Component, IEnumerable
The IEnumerable interface requires implementation of the GetEnumerator() method. The enumerator is responsible for keeping track of the position in the underlying collection and indicating if there are more items to be iterated over.
This is implemented in Transform below
public IEnumerator GetEnumerator()
{
return new Transform.Enumerator(this);
}
private class Enumerator : IEnumerator
{
Transform outer;
int currentIndex = -1;
internal Enumerator(Transform outer)
{
this.outer = outer;
}
//*undocumented*
public object Current
{
get { return outer.GetChild(currentIndex); }
}
//*undocumented*
public bool MoveNext()
{
int childCount = outer.childCount;
return ++currentIndex < childCount;
}
//*undocumented*
public void Reset() { currentIndex = -1; }
}
public class noorderedlist {
node head;
public void afadd(int element){
node newnode=new node(element);
if(head==null){
head=newnode;
return;
}
node temp=head;
while(temp.next != null){
temp = temp.next;
}
temp.next = newnode;
}
public void print(){
node currentnode=head;
while(currentnode!=null){
System.out.print(currentnode.element);
currentnode=currentnode.next;
}
public class node {
node next=null;
int element;
public node(int element){
this.element=element;
}
i want to write method to add point in a single link list,it works but i have a problem.why the head will change after the change of the temp?i hear about that is the shallow copy,but why the shallow copy does not work in"temp=temp.next"?,according to that in the loop the temp is changing then the head should change like "head=temp.next", but when i execute the print method the element of the head does not change but it adds a new point in the end of the link list. so what's going on here?
My application needs only fixed no of records to be read
& processed. How to limit this if I am using a flatfileItemReader ?
In DB based Item Reader, I am returning null/empty list when max_limit is reached.
How to achieve the same if I am using a org.springframework.batch.item.file.FlatFileItemReader ?
For the FlatFileItemReader as well as any other ItemReader that extends AbstractItemCountingItemStreamItemReader, there is a maxItemCount property. By configuring this property, the ItemReader will continue to read until either one of the following conditions has been met:
The input has been exhausted.
The number of items read equals the maxItemCount.
In either of the two above conditions, null will be returned by the reader, indicating to Spring Batch that the input is complete.
If you have any custom ItemReader implementations that need to satisfy this requirement, I'd recommend extending the AbstractItemCountingItemStreamItemReader and going from there.
The best approch is to write a delegate which is responsible to track down number of read records and stop after a fixed count; the components should take care of execution context to allow restartability
class CountMaxReader<T> implements ItemReader<T>,ItemStream
{
private int count = 0;
private int max = 0;
private ItemReader<T> delegate;
T read() {
T next = null;
if(count < max) {
next = delegate.read();
++count;
}
return next;
}
void open(ExecutionContext executionContext) {
((ItemStream)delegate).open(executionContext);
count = executionContext.getInt('count', 0);
}
void close() {
((ItemStream)delegate).close(executionContext);
}
void update(ExecutionContext executionContext) {
((ItemStream)delegate).update(executionContext);
executionContext.putInt('count', count);
}
}
This works with any reader.
public class CountMaxFlatFileItemReader extends FlatFileItemReader {
private int counter;
private int maxCount;
public void setMaxCount(int maxCount) {
this.maxCount = maxCount;
}
#Override
public Object read() throws Exception {
counter++;
if (counter >= maxCount) {
return null; // this will stop reading
}
return super.read();
}
}
Something like this should work. The reader stops reading, as soon as null is returned.
PLEASE HELP ME TO FIND THIS ANSWER
NULL POINTER EXCEPTION ERROR HELP ME
on these two lines
25,83
null pointer exception please correct my code
i created a object l with reference to class linkk
to access methods in the class
but while accessing the methods in the class with different conditions
it is showing null pointer exception
i didnt finish the code due to this error im struck at this point i cant move
further
this is my post
in overflow
i have read answers in overflow but this is the
first time fr me to post a question in overflow ,
today i created a ac nd posting this question please help me frnds
import java . util.Scanner;
class node
{
int i,q;
node next;
node prev;
}
class link{
public static void main(String args[])
{
linkk l = new linkk();
l.op();
int user=0;
while(user!=10)
{Scanner a=new Scanner(System.in);
if(user==1)
{
System.out.println("\nenter data\n");
l.create(a.nextInt());
}System.out.println("\n1.create link\n2.insert beginning\n3.insert middle\n4.insert end\n5.delete data\n6.reverse");
user=a.nextInt();
}
if(user==2)
l.insertbeg();
if(user==3)
l.insertmid();
if(user==4)
l.insertend();
if(user==5)
l.del();
if(user==6)
l.reverse();
if(user==7)
l.display();
}
}
class linkk
{
node temp4;
int ch,add,cnt=0,t=0,b;
node p= new node();
node q;
node last;
node first=null;
public boolean isEmpty()
{
return first == null;
}
public void insertbeg()
{
}
public void insertmid()
{
}
public void insertend()
{
}
public void del()
{
}
public void reverse()
{
}
public void display()
{
}
public void create(int val)
{
first.i=val;
first.next=null;
cnt++;
}
public void ob()
{
}
public void op()
{
}
}
Your defined first as null as node first=null; and you are trying to access i with first object using first.i=val; by calling l.create(a.nextInt());.
You should initialize first as below:
node first = new node();//and then access i of it and so on.
I'm trying to find a method that allows me to do a rollback when one of the elements of a list fails for a reason within the business rules established (ie: when throw my customize exception)
Example, (the idea is not recording anything if one element in list fails)
public class ControlSaveElement {
public void saveRecords(List<MyRecord> listRecords) {
Boolean status = true;
foreach(MyRecord element: listRecords) {
// Here is business rules
if(element.getStatus() == false) {
// something
status = false;
}
element.persist();
}
if(status == false) {
// I need to do roll back from all elements persisted before
}
}
...
}
Any idea? I'm working with Roo 1.2.2..
What you're describing is a service method (saveRecords) that needs to be transactional. Either annotated with the #Transactional annotation and then you raise an exception, or you will have to look into using the TransactionTemplate to get finer control in order to do a manual rollback.
http://static.springsource.org/spring/docs/3.1.x/spring-framework-reference/html/transaction.html
http://springinpractice.com/2008/03/18/annotation-based-transactions-in-spring/
is there a way to force a transactional rollback without encountering an exception?
How about creating a new static method in the MyRecord entity:
#Transactional
public static void saveMyRecordsList(List<MyRecord> listRecords) {
boolean persistAll = true;
foreach(MyRecord element: listRecords) {
if(element.getStatus() == false) {
persistAll = false;
}
}
if (persistAll) {
foreach(MyRecord element: listRecords) {
entityManager().persist(element);
}
}
}
This may be more efficient than persisting elements and having to roll them back?