Question

I have a Map and a List My list a master list of some value object and Map contains keys which are id of the value object
I have a value object

 public class Value
{


    private int id;

    private String value;

//set and gets to follow
}

Map valueMap = new HashMap();   

valueMap.put(1001,"Test1")//key is id of the value object 
valueMap.put(1002,"Test2")
valueMap.put(1003,"Test3")


 List list = new Array list();
 list.add(value1)
 list.add(value2)
 list.add(value3)
 list.add(value4)
 list.add(value5)

From the list i want to extract a subset of list whose value.id is ==key of map

how can i do and iterate over both?

Answer 1

You should use

Map<Integer, String> valueMap = new HashMap<>();

and

List<Value> list = new ArrayList<>();

Then, you can do something like this:

List<Value> subset = new ArrayList<>();
Iterator<Value> iterator = list.iterator();
while (iterator.hasNext()) {
    Value val = iterator.next();
    if (valueMap.containsKey(val.getId())) {
        subset.add(val);
    }
}

or even

List<Value> subset = new ArrayList<>();
for (Value val : list) {
    if (valueMap.containsKey(val.getId())) {
        subset.add(val);
    }
}