The Interface and Class Hierarchy Diagram of Java Collections

1. Collection vs Collections

First of all, "Collection" and "Collections" are two different concepts. As you will see from the hierarchy diagram below, "Collection" is a root interface in the Collection hierarchy but "Collections" is a class which provide static methods to manipulate on some Collection types.

2. Class hierarchy of Collection

The following diagram demonstrates class hierarchy of Collection.

3. Class hierarchy of Map

Here is class hierarchy of Map.

4. Summary of classes

collection-summary

5. Code Example

The following is a simple example to illustrate some collection types:

List<String> a1 = new ArrayList<String>();
a1.add("Program");
a1.add("Creek");
a1.add("Java");
a1.add("Java");
System.out.println("ArrayList Elements");
System.out.print("\t" + a1 + "\n");
 
List<String> l1 = new LinkedList<String>();
l1.add("Program");
l1.add("Creek");
l1.add("Java");
l1.add("Java");
System.out.println("LinkedList Elements");
System.out.print("\t" + l1 + "\n");
 
Set<String> s1 = new HashSet<String>(); // or new TreeSet() will order the elements;
s1.add("Program");
s1.add("Creek");
s1.add("Java");
s1.add("Java");
s1.add("tutorial");
System.out.println("Set Elements");
System.out.print("\t" + s1 + "\n");
 
Map<String, String> m1 = new HashMap<String, String>(); // or new TreeMap() will order based on keys
m1.put("Windows", "2000");
m1.put("Windows", "XP");
m1.put("Language", "Java");
m1.put("Website", "programcreek.com");
System.out.println("Map Elements");
System.out.print("\t" + m1);

Output:

ArrayList Elements
	[Program, Creek, Java, Java]
LinkedList Elements
	[Program, Creek, Java, Java]
Set Elements
	[tutorial, Creek, Program, Java]
Map Elements
	{Windows=XP, Website=programcreek.com, Language=Java}

If you want someone to read your code, please put the code inside <pre><code> and </code></pre> tags. For example:

<pre><code> 
String foo = "bar";
</code></pre>

sud on 2012-2-3

it is helpful
Shibi on 2013-9-13

Excellent illustration. Thanks a lot.
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Mdhar on 2013-10-24

Very good explanation with clear diagrams. Thanks.
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kai ran on 2013-11-25

Clear explanation, great work!
Bortnikov on 2013-11-29

You forget
interface NavigableMap
Li Yang on 2013-12-14

The graph is very clear~
Ankit Gupta on 2014-2-11

great explanation… very useful….
Vijay on 2014-3-10

It is very crisp and clear..
智陶 on 2014-3-28

u missed the abstractinterface,such as abstractcollection,abstractset,abstractlist,Those are important in the hierarchy of java collection.
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gowtham Bk on 2016-2-15

If I wanna add BST to the collection. where should it come?

The Interface and Class Hierarchy Diagram of Java Collections

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