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Stack of Plates: Cracking the coding interview , Personal Solution [closed]

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Stack of Plates: Imagine a (literal) stack of plates. If the stack gets too high, it might topple.
Therefore, in real life, we would likely start a new stack when the previous stack exceeds some threshold. Implement a data structure SetOfStacks that mimics this. SetOfStacks should be composed of several stacks and should create a new stack once the previous one exceeds capacity.
SetOfStacks. push () and SetOfStacks. pop() should behave identically to a single stack (that is, pop ( ) should return the same values as it would if there were just a single stack).
I've implemented a solution with a HashMap.
I'd like to know if this is a good implementation (in space and complexity) and if it can be improve. Moreover, I've used correctly this.index ?
public class SetOfStacks {
private final int LIMIT= 5;
private HashMap<Integer,Stack<Integer>> setOfStack;
private int index;
public SetOfStacks(){
this.setOfStack= new HashMap<>();
this.index = 0;
}
public void addStack(){
this.index++;
if(!setOfStack.containsKey(index))
this.setOfStack.put(index, new Stack<Integer>());
}
public void pushElement(int value){
if (isFull())
addStack();
setOfStack.get(index).push(value);
}
public boolean isFull(){
return setOfStack.get(index).size() == LIMIT;
}
public void popElement(){
if(setOfStack.get(index).isEmpty())
index--;
setOfStack.get(index).pop();
}
public int peekElement(){
return setOfStack.get(index).peek();
}
}
FOLLOW UP
Implement a function popAt (int index) which performs a pop operation on a specific substack.
I didn't write the solution for it, but i think that his implementation should be easy. I only need to pass the parameter and just manage the push/pop, in case i need to refull that stack or not.
What do you think about maintenance of my code if you need to implement the follow up?

It's good but you have some mistake,
you never initialize the first stack,
also what happens if I initialize the SetOfStacks and call the pop?(assuming you fixed the first mistake)

I need to exit a methode, without returning a value [closed]

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I have methode that returnd the smallest value in an arrayList. However, it should return anything if the arrayList is empty. Is there something I can do?
private int smallest() {
if(alList.empty()) {
//whatever will exit the
//function.
}
small = alList.get(0);
for(int i = 1, i <
alList.size(), i++) {
if(small > alList.get(i)){
small = alList.get(i)
}
}
return small;
}
//Thanks for your help.

Since you need to return an int, then no, you must return a value.
If you can change the method signature, you can:
Return an Integer and so return null.
Return Optional<Integer> and return an empty Optional.

There are many options. The three most obvious ones:
throw an exception: `if (alList.isEmpty()) throw new IllegalStateException("alList must not be empty when invoking smallest()");
decide on a sentinel value, for example 0, and return that. Update the docs to make it clear that 0 is returned for empty lists.
private int smallest(int valueIfEmpty) { if (alList.isEmpty()) return valueIfEmpty; ... } - i.e. pass the value to be returned in that case, so that the caller can decide what should happen.

How to debug an if statement that is not working? [closed]

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import java.util.*;
public class ass {
public static void main(String[] args) {
// TODO Auto-generated method stub
String[]c={"sid","is","cool"};
List<String>list1=new ArrayList<String>();
for(String w:c){
list1.add(w);
}
String[]q={"is"};
List<String>list2=new ArrayList<String>();
for(String t:q){
list2.add(t);
}
EditList(list1,list2);
for(int i=0;i<list1.size();i++){
System.out.printf("%s ", list1.get(i));
}
}
public static void EditList(Collection<String>l1, Collection<String>l2){
Iterator<String>it=l1.iterator();
while(it.hasNext()){
if(l2.contains(it.next()));
it.remove();
}
}
}
In this programme I have two lists. I wanted to remove the items that are common in the first and second list from the first list and print it. I don't want a workaround or any other code suggestions. Can someone please explain why my code is not working?
I am following New Boston's tutorials.

Here:
if(l2.contains(it.next()));
it.remove();
That semicolon after if is a real statement.
Thus it.remove() happens always; like if ... that if not there!
Thus the real answer: always always always use
if (){
stuff
}
... even for single statements! Same for loops!

try
public static void EditList(Collection<String>l1, Collection<String>l2){
Iterator<String>it=l1.iterator();
while(it.hasNext()){
String current=it.next();
if(l2.contains(current)){
i1.remove(current); // assuming u wish to remove from l1
}
}
}

Pass boolean value to another class [closed]

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In my main class I want to check if there was a change by using a boolean variable:
public class Main {
private boolean change = false;
public boolean getChange() {
return change;
}
public void setChange(boolean change) {
this.change = change;
}
private void method1() {
// some command
setChange(true);
method1();
}
If I want to get this boolean value in my second class, I always get returned "false", no matter if my method1 ran or not.
public class BoolTest {
Main m = new Main();
System.out.println(m.getChange()); // returns "false"
}

You must have two instances of Main. Use the same one. Example:
Main m = new Main();
System.out.println(m.getChange());
m.setChange(true);
System.out.println(m.getChange());
You probably want to share the same instance over multiple classes. Pass the instance to the other classes and use them as expected.

What does mean, lines.next.toInt in Java [closed]

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What does mean this line in java:
m = lines.next.toInt
Thanks.

You can get this done in java using any reader. e.g- BufferedReader, FileReader anything like this.
public class InJava
{
BufferedReader br= new BufferedReader(new InputStreamReader(System.in));
//
//in main()
public static void main(String [] args)
{
Object obj= br.readLine();
}
}
If you are using a list use Iterator.
public class InJava
{
List<double> lst= new ArrayList<double>();
//fill the list.
Iterator it= lst.iterator();
//in main()
while(it.hasNext())
{
Object obj= it.next();
//Continue
}
}

lines is perhaps an iterable collection of Double objects. The code that you've posted accesses the next element in sequence and converts it to an integer.
If you can post the surrounding code as well, we could get more context on the same.