Iterating of Generic Collections in Java

Question

I'm very new to Java and struggling to understand generics, the ways they can be used, and the syntax for doing so.

I've the following class

class MyCustomArray<T>{

    private T[] myArray;

    // Default Constructor
    public ArraySet(){
        this.myArray= (T[]) new Object[10];
    }

    // Method to get array length
    public int getSize(){
        return this.myArray.length;
    }

    ... some random code

    // Method to iterate
    public void iterateSomehow(MyCustomArray<? extends T> collection){

        // doesn't work
        for(T obj: collection){...}

        // doesn't work
        for(int i=0; i< collection.size(); i++){
            T nextObj= collection[i];
        }

    }
}

This is for a class assignment, which disallows the use of standard classes like ArrayList . I feel like I'm missing something fundamental here, but don't know what.

Is my approach wrong? Is it just syntactical?

Some more context:

My immediate goal is to check each value in the given collection object as such (psuedo-code, clearly):

for( int i=0; i < collection.length; i++ ):
    value = collection[i];
    if (value == badValue):
       // whatever

Answer 1

Only arrays can be indexed with the [] syntax, and only arrays or classes implementing Iterable can be used in the right hand side of an enhanced for loop ( for (T xxx: yyy) ). Your class is not an array and does not implement Iterable , so neither of your attempts worked.

Your class contains an array though - myArray . You can just iterate through that. Both of these are fine:

for(T obj: collection.myArray){...}
// or
for(int i=0; i< collection.getSize(); i++){
    T nextObj= collection.myArray[i];
}

I also feel like your method should not have the parameter and should iterate over this instead (if this is actually a requirement of the homework, then it can't be helped):

for(T obj: myArray){...}

for(int i=0; i< getSize(); i++){
    T nextObj= myArray[i];
}

Answer 2

You can't iterate though collection directly(because it's just object) you should access to myArray. You also can implement Iterable interface, it's allows you something like this

  for(T obj: collection){...}

https://www.geeksforgeeks.org/java-implementing-iterator-and-iterable-interface/