I encountered a problem when I tried to run the following code:
ArrayList paretoSet=new ArrayList(); // contains a collection of ArrayList
ArrayList<Integer> toPass=new ArrayList<Integer>();
int[] fParetoSet=new int[ParetoSet.size()];
int[] gParetoSet=new int[ParetoSet.size()];
for (int i=0;i<paretoSet.size();i++){
toPass.clear();
toPass.add((Integer)paretoSet.get(i));
int [] totake=calculate(toPass);
fParetoSet[i]=totake[0];
gParetoSet[i]=totake[1];
}
` where claculate(ArrayList x) is a method that takes an integer arraylist and returns an integer array. I can not make Paretoset an integer arraylist as it creates problem in other parts of my program. I encountered an exception in the line toPass.add((Integer)paretoSet.get(i));
as java.lang.ClassCastException: java.util.ArrayList cannot be cast to java.lang.Integer How should I fix this problem?
Thanks in advance
If ParetoSet is a collection of ArrayList, then the call ParetoSet.get(i) will return the ArrayList at index i. As the error says, an ArrayList is not a a type of Integer and cannot be cast to one.
Other points of interest:
pareToSetParetoset has been declared with a raw typenew ArrayList<Integer>() redundant since JDK7EDIT
paretoSet, as per Jim's commentsEDIT
An ArrayList is neither conceptually, or actually an Integer. If you say the sentence 'A list is a type of integer' it doesn't make sense. If we check the javadoc for ArrayList we can see that its inheritance tree is:
java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractList<E>
java.util.ArrayList<E>
All Implemented Interfaces:
Serializable, Cloneable, Iterable<E>, Collection<E>, List<E>, RandomAccess
So we can say for example that ArrayList is a type of AbstractList, or AbstractCollection, but not an Integer as Integer is not part of its lineage.
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