Java

TOPIC 20 – JAVA COLLECTIONS II - SETS

LESSON NOTE

SETS

Sets are data structures with the following characteristics:

• No duplicate values are stored in the set.
• There is no guaranteed ordering of elements.
• One can add and remove elements based on their value.
• One can check if a value is in the set.

JAVA IMPLEMENTATIONS

We will consider two different implementations. Their class names are:

• TreeSet
• HashSet

For now, we will not worry about the pros and cons of the implementations because we haven't discussed trees or hash functions. All you need to know is there are two different implementations that allow you to work with a Set structure.

IMPORTANT METHODS

Here are important Java methods:

• add – adds an element to the set if its not a duplicate
• contains – returns true if the specified value is already in the set
• remove – Removes an element from the set
• addAll – adds all elements of a provided collection to the set
• clear – empties the set

TreeSet<Integer> set = new TreeSet<Integer>();

System.out.println(set);

set.add(4);

set.add(5);

System.out.println(set);

set.add(2);

System.out.println(set);

set.add(4);

System.out.println(set);

set.remove(2); //removes the value 2

System.out.println(set);

if(set.contains(4))

System.out.println("Four is in there!");

else

System.out.println("Not in there");

[]

[4, 5]

[2, 4, 5]

[2, 4, 5]

[4, 5]

Four is in there!