Diamond operator was introduced in Java 7 as a new feature. The main purpose of the diamond operator is to simplify the use of generics when creating an object. It avoids unchecked warnings in a program and makes the program more readable.
It is called that because <> looks like a diamond if you tilt your head to the side.
```
HashMap<String, HashMap<String, String>> map1 = new HashMap<String, HashMap<String, String>>(); // Without <>
HashMap<String, HashMap<String, String>> map2 = new HashMap<>(); // With <>
```