Java Collection Best Practices

1. Decide approximate initial capacity of a collection -  As Collection implementations like ArrayList, HashMap, use Array internally for storing, you can speed up things  by setting initial capacity.

2. Use ArrayLIst, HahMap etc instead of Vector , HashTable to avoid synchronization overhead. Even better use array where ever possible.

3. Program to interface instead of implementation – It gives freedom of switching implementation without touching code.

For Example : Use

List list = new ArrayList();

Avoid :

ArrayList list = new ArrayList();

4. Always return empty collection object instead of null .

For Example : Use

public List getCustomer(){
        //...
        return new ArrayList(0);
}

Avoid :

public List getCustomer(){
        //...
        return null;
    }

5. Generally you use a java.lang.Integer or
a java.lang.String class as the key, which are immutable Java objects.

6. Avoid exposing collection field – Always provide fine grained methods for collection fields instead of directly exposing setter/getter for collection field.

For Example Use :

class  Order
{
    List ArrayLisy itemList;
    //...

    public boolean addItem(Item item){
        //....
    }

    public boolean removeItem(Item item){
        //....
    }
}

Avoid :

class  Order
{
    List ArrayLisy itemList;
    //...

    public void setItems(List items){
        //....
    }

  }

7. Avoid storing unrelated or different types of objects into same collection

For Example Use :

public class  Order
{
    List ArrayLisy itemList;
    //...

    public boolean addItem(Item item){
        //....
    }

    public boolean removeItem(Item item){
        //....
    }

    public static void main(String [] args){
        int id;
        String desc;
        Order order = new Order();
        //...

        Item item = new Item()[
        item.setItem(new Integer(id));
        item.setDesc(dec);
        order.addItem(item);
        //...
    }

}

public class Item
{
    int id;
    String desc;

    public void setId(int id){
        //..
    }

    public int getId(){
        //..
    }

    public void setDesc(){
        //..
    }

    public String getDesc(){
        //..
    }
}

Avoid :

public class  Order
{
    List ArrayLisy itemList;
    //...

    public boolean addItem(Item item){
        //....
    }

    public boolean removeItem(Item item){
        //....
    }

    public static void main(String [] args){
        int id;
        String desc;
        Order order = new Order();
        //...

        List item = new ArrayList()[
        item.add(new Integer(id));
        item.add(dec);
        order.addItem(item);
        //...
    }

   }

8. Use Collection framework features instead of traditional approach.

For Example: Use

//search for duplicate names
for (int i=0;i<nameArray.length ;i++ )
{
    String name = nameArray[i];
    if(nameSet.contains(name)){
        System.out.println("Got Duplicate name = " + name );
    }
}

Avoid:

//search for duplicate names

for (int i=0;i<nameArray.length ;i++ )
{   
    String name = nameArray[i];
    for(int j=0;j<nameArrayLength;j++){
        if(nameArray[j].equals(name)){
            System.out.println("Got Duplicate name = " + name );
        }
    }
}