CODEWITHSUNDEEP
javaarraylistcollections
Akshma Mittal
Akshma Mittal

Reputation: 89

collection in java(How to print objects separately)

If we are working on collection....for example ArrayList then if ArrayList contains two types of objects(Integer and String) and we want to print them separately like integer objects in one group and string objects in another group. Please anyone tell me how can we do this?

Upvotes: 1

Views: 185

Answers (2)

Joby Wilson Mathews
Joby Wilson Mathews

Reputation: 11126

May be below program can help you , it will dynamically create separate list of a type depending upon the object in your main list.

import java.util.ArrayList;
import java.util.HashMap;
import java.util.Map;

public class SeparateType {

    public static void main(String[] args) {
        ArrayList<Object> arrayList=new ArrayList<>();
        arrayList.add(101);
        arrayList.add("Hello");
        arrayList.add(102);
        arrayList.add("World");
        arrayList.add(103);
        arrayList.add("String3");
        arrayList.add(104);
        arrayList.add("String4");
        arrayList.add(1.0);

        for (Map.Entry<Class,ArrayList<Object>> entry : convertToSeprateType(arrayList).entrySet()) {
            System.out.println(entry.getKey().getSimpleName()+ " List values : " + entry.getValue());
        }
    }

    public static <T> HashMap<Class,ArrayList<Object>>  convertToSeprateType(ArrayList<Object> arrayList) {
        HashMap<Class,ArrayList<Object>> hashMap=new HashMap<>();
        final T val;
        for(Object object:arrayList) {
            if(hashMap.containsKey(object.getClass())) {
                hashMap.get(object.getClass()).add(object);
            }else {
                ArrayList<T> list=new ArrayList<T>();
                list.add((T) object);
                hashMap.put(object.getClass(), (ArrayList<Object>) list);

            }

        }
        return hashMap;
    }

}

Output:

Integer List values : [101, 102, 103, 104]
Double List values : [1.0]
String List values : [Hello, World, String3, String4]

Upvotes: 0

Shubhendu Pramanik
Shubhendu Pramanik

Reputation: 2751

You can use List<Object> but in that case you need to be careful. Have to check which instance it is and cast it accordingly.

See below example:

EDIT

added list for each group 

List<Object> list = new ArrayList<>();
    list.add("a");
    list.add(2);

    List<String> strList = new ArrayList<>();
    List<Integer> intList = new ArrayList<>();

    for (Object o : list) {
        if (o instanceof String) {
            System.out.println("String is: " + o);
            strList.add((String) o);
        }
        if (o instanceof Integer) {
            System.out.println("Integer is: " + o);
            intList.add((Integer) o);
        }
    }

OP:

String is: a
Integer is: 2

Upvotes: 1

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