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java generics: can't create a simple print array method


java generics: can't create a simple print array method

By : user2953205
Date : November 20 2020, 01:01 AM
this will help When it comes to generics, Java makes a difference between primitive types and types derived from java.lang.Object. Only non-primitive types can be used as arguments of generic methods. Since int is not generic, printArray does not apply to it.
You can fix it by providing an overload for int, or by making integerArray an Integer[]:
code :
Integer[] integerArray = {1,2,3,4,5};
printArray(integerArray);


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Java Arraylist.Using Generics and Wildcards to create a reusable method

Java Arraylist.Using Generics and Wildcards to create a reusable method


By : Seng Santphallin
Date : March 29 2020, 07:55 AM
around this issue I am creating a reusable method that returns an array-list. , Try this :
code :
public abstract class TypeBase {

}

public class TypeOne extends TypeBase {
    public TypeOne(String val1, String val2) {
        // TODO Auto-generated constructor stub
    }
}

public class TypeTwo extends TypeBase {
    public TypeTwo(String val1, String val2, int val3, boolean val4) {
        // TODO Auto-generated constructor stub
    }
}

public <T extends TypeBase> List<T> getReusable(int method) {
    List<T> mResuableList = new ArrayList<T>();
    switch (method) {
    case 1:
        mResuableList.add((T) new TypeOne("TypeOne", "TypeOneID"));
        break;
    case 2:
        mResuableList.add((T) new TypeTwo("TypeTwo", "TypeTwoID", 1234, true));
        break;
    default:
        break;
    }
    return mResuableList;
}

public class UsingClass{
    public void callReusable(){
        List<TypeOne> lstOne = getReusable(1);
        List<TypeTwo> lstTwo = getReusable(2);
    }
}
Java Generics: create a general method operating on parent classes

Java Generics: create a general method operating on parent classes


By : user3340782
Date : March 29 2020, 07:55 AM
it should still fix some issue the problem here is that Java does not allow downcasting. You should create new Objects of the childclasses instead of returning new Objects of the parent class.
The parseERType Method should look something like this:
code :
HERMEntityRelationshipType parseERType(DBMEntityRelationshipType   dbmERType){
    if(dbmERType.getClass().equals(DBMEntityType.class)) {
        return new HERMEntityType(dbmERType);
    } else {
        return new HERMRelationshipType(dbmERType);
    }

}
How Can I create method which use Java generics put the maps key to list?

How Can I create method which use Java generics put the maps key to list?


By : Kiairus Diamond
Date : March 29 2020, 07:55 AM
Does that help , Maybe your map is empty, because the example below works:
code :
public class Utils {

    public <T, K> List<T> map2list(Map<T, K> map) {
        List<T> list = new ArrayList<T>(map.keySet());
        return list;
    }

    /**
     * @param args
     */
    public static void main(String[] args) {
        Map<String, Integer> map = new HashMap<String, Integer>();
        map.put("test1", 1);
        map.put("test2", 2);
        map.put("test3", 3);
        Utils t = new Utils();
        List<String> result = t.map2list(map);
        for (String key : result) {
            System.out.println(key);
        }
    }

}
How to create an ensureCapacity method that deals with Array Generics in Java

How to create an ensureCapacity method that deals with Array Generics in Java


By : David
Date : March 29 2020, 07:55 AM
I wish this help you So, I am creating a generic data structure named "Sack". In this I add items to a sack, grab a random item, see if it's empty, or dump out its contents etc. Also I'm creating it to expand to hold as many items as needed. , I figured it out, here's what the solution is to my question.
code :
private void ensureCapacity(int capacity)
{
    if (elementData.length < capacity)
    {
        int newCapacity = elementData.length * 2 + 1;
        elementData = Arrays.copyOf(elementData, newCapacity);
    }
}
How to create a grab method in Java that deals with Generics and Arrays

How to create a grab method in Java that deals with Generics and Arrays


By : user2486922
Date : March 29 2020, 07:55 AM
I wish did fix the issue. I don't understand why your grab method returns an array instead of a single element. I can suggest you a different approach
code :
public class Sack<E> {
    private final static int DEFAULT_CAPACITY = 10;
    private final static float REALLOC_FACTOR = 1.5f;
    private E[] elementData;
    private int size;

    public Sack() {
        this(DEFAULT_CAPACITY);
    }
    @SuppressWarnings("unchecked")
    public Sack(int capacity) {
        if(capacity <= 0)
            throw new IllegalArgumentException("capacity " + capacity);
        elementData = (E[]) new Object[capacity];
    }
    public boolean isEmpty() {
        return size == 0;
    }
    public void add(E item) {
        int index = size++;
        if(size > elementData.length-1)
            elementData = Arrays.copyOf(elementData, (int)(size*REALLOC_FACTOR));
        elementData[index] = item;
    }
    public E [] dump() {
       E [] E2 = Arrays.copyOf(elementData, size);
       Arrays.fill(elementData, null);
       size = 0;
       return E2;
    }
    public E grab() {
        if(size == 0)
            return null;
        int index = (int)(Math.random()*size);
        E element = elementData[index];
        elementData[index] = elementData[size-1];
        elementData[size-1] = null;
        size--;
        return element;
    }
}
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