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Thread: HashSet cannot be cast to java.util.ArrayList

  1. #1
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    Default HashSet cannot be cast to java.util.ArrayList

    public class Employee{
     
        private int id;
        private String name;
        private String address;
        private double salary;
    //setter & getter
    }

    public class test{
     
    		ArrayList check= coll (); 
    		CheckCollection(check);
     
    public static ArrayList coll (){
     
    		ArrayList list = new ArrayList();
    		Set set = new HashSet();
     
    Employee ts1 = new Employee (10, "Jad", "L.A", 200.0);
            Employee ts2 = new Employee (11, "Amal", "Berlin", 600.0);
            Employee ts3 = new Employee (12, "Jasmin", "London", 250.0);
            Employee ts4 = new Employee (10, "sam", "Paris", 200.0);
            Employee ts5 = new Employee (14, "Adam", "NY", 210.0);
     
    set.add(ts1);
    set.add(ts2);
    set.add(ts3);
    set.add(ts4);
    set.add(ts5);
     
    //now convet the Set to List
    list.add(set);
     
    return list;
    }
     
    public static void CheckCollection(ArrayList data) {
    ArrayList xxx= null;
    for (int i = 0; i < data.size(); i++) {
     
    	       	    xxx = (ArrayList)data.get(i);
    }
    }

    any way when i run it i get error:
    HTML Code:
    java.lang.ClassCastException: java.util.HashSet cannot be cast to java.util.ArrayList
    so why i thought i could convert the Set totally to List Type !!


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    Default Re: HashSet cannot be cast to java.util.ArrayList

    Are you asking us why you thought what you thought? We can't answer that.

    If you're also wondering how to convert a HashSet to an ArrayList, here's an example of how to do that:
    // found here:
    // http://www.xyzws.com/javafaq/how-to-convert-a-hashset-to-an-arraylist/180
     
    import java.util.ArrayList;
    import java.util.HashSet;
    import java.util.List;
    import java.util.Set;
     
    public class TestClass {
     
      public static void main(String[] args) {
     
        Set<String> hashset = new HashSet<String>();
        hashset.add("A");
        hashset.add("B");
        hashset.add("C");
        List<String> list = new ArrayList<String>(hashset);
        System.out.println(list.toString());
     
      }
    }

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    Default Re: HashSet cannot be cast to java.util.ArrayList

    ok the same what i did, i also make the same
    ArrayList list = new ArrayList(set);
    but still get the error

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    Default Re: HashSet cannot be cast to java.util.ArrayList

    This thread has been cross posted here:

    http://www.java-forums.org/new-java/80700-hashset-cannot-cast-java-util-arraylist.html

    Although cross posting is allowed, for everyone's benefit, please read:

    Java Programming Forums Cross Posting Rules

    The Problems With Cross Posting


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    Default Re: HashSet cannot be cast to java.util.ArrayList

    If you want help with updated code, please post it. We can't accurately imagine what you've done.
    ArrayList list = new ArrayList(set);
    but still get the error[/QUOTE]
    No, that change is not equivalent to what I posted. This is:
    public class TestClass
    {
        // modified to simply make the point, not provide the same function
        public static void coll()
        {
            Set<Employee> set = new HashSet<Employee>();
     
            Employee ts1 = new Employee (10, "Jad", "L.A", 200.0);
            Employee ts2 = new Employee (11, "Amal", "Berlin", 600.0);
            Employee ts3 = new Employee (12, "Jasmin", "London", 250.0);
            Employee ts4 = new Employee (10, "sam", "Paris", 200.0);
            Employee ts5 = new Employee (14, "Adam", "NY", 210.0);
     
            set.add(ts1);
            set.add(ts2);
            set.add(ts3);
            set.add(ts4);
            set.add(ts5);
     
            //now convet the Set to List and print the results
            ArrayList<Employee> list = new ArrayList<Employee>(set);
            System.out.println( list.toString() );
     
            // this is your old line, commented out
    //        list.add(set);
     
        } // end method coll()
     
        public static void main( String[] args )
        {
            coll();
        }
    }

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