编译警告：使用未经检查或不安全的操作

Question

When I want to build a jar file using artifacts I get the following error:

Warning:java: Note: /Users/doekewartena/IdeaProjects/LemmingsWalker/Java-Base/src/com/github/lemmingswalker/ListDivisor.java uses unchecked or unsafe operations. Warning:java: Note: Recompile with -Xlint:unchecked for details.

I still get a jar file but I have problems in another project which I think are related to this. I have seen solutions on stackoverflow. Most of the times people seem to use new ArrayList() instead of new ArrayList<TheType>() . In my case, it might be something similar, but I can't finds it. I hope someone can.

public class ListDivisor<T> {

    List<T> list;

    int subListStartIndex = 0;
    int currentGetIndex = 0;

    InstanceHelper instanceHelper;


    public ListDivisor(List<T> list, InstanceHelper<T> instanceHelper) {
        this.list = list;
        this.instanceHelper = instanceHelper;
    }

    // . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


    public void reset() {
        subListStartIndex = 0;
        currentGetIndex = 0;

        if (instanceHelper.doResetInstances()) {
            for (T obj : list) {
                instanceHelper.resetInstance(obj);
            }
        }
    }

    // . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


    public SubListGetter<T> getSubListGetter(int size) {

        int fromIndex = subListStartIndex; // inclusive
        int toIndex = fromIndex + size; // exclusive

        for (int i = list.size(); i < toIndex; i++) {
            list.add((T) instanceHelper.createInstance());
        }

        subListStartIndex = toIndex;
        currentGetIndex = toIndex;

        //return list.subList(fromIndex, toIndex);
        return new SubListGetter(fromIndex, toIndex, list);
    }

    // . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

    /**
     * Returns a subList starting where the previous subList ended till
     * the latest object added till then.
     *
     * @return
     */
    public SubListGetter<T> getSubListGetter() {
        return getSubListGetter(currentGetIndex - subListStartIndex);
    }

    // . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


    public T getNext() {

        if (currentGetIndex >= list.size()) {
           list.add((T)instanceHelper.createInstance());
        }

        return list.get(currentGetIndex++);

    }

    // . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .


    public void clear() {
        list.clear();
        reset();
    }


    // =====================================================================

    public interface InstanceHelper<T> {
        public T createInstance();
        public boolean doResetInstances();
        public void resetInstance(T obj);
    }

    // =====================================================================


}

And the SubListGetter class:

public class SubListGetter<T> {

    int fromIndex, toIndex;
    List<T> target;

    public SubListGetter (int fromIndex, int toIndex, List<T> target) {
        this.fromIndex = fromIndex;
        this.toIndex = toIndex;
        this.target = target;
    }

    public List<T> getSubList() {
        return target.subList(fromIndex, toIndex);
    }

}

Answer 1

The field instanceHelper is a raw type of InstanceHelper . You should use the type parameter T :

InstanceHelper<T> instanceHelper;

You can remove the casting to T once that's complete:

for (int i = list.size(); i < toIndex; i++) {
   list.add(instanceHelper.createInstance());
}