Java TreeMap - firstKey() Method
The java.util.TreeMap.firstKey() method returns the first (lowest) key currently in this map.
Syntax
public K firstKey()
Here, K is the type of key maintained by the container.
Parameters
No parameter is required.
Return Value
Returns the first (lowest) key currently in this map.
Exception
Throws NoSuchElementException, if this map is empty.
Example:
In the example below, the java.util.TreeMap.firstKey() method returns the first (lowest) key in the given map.
import java.util.*;
public class MyClass {
public static void main(String[] args) {
//creating a treemap
TreeMap<Integer, String> MyMap = new TreeMap<Integer, String>();
//populating the map
MyMap.put(102, "John");
MyMap.put(103, "Marry");
MyMap.put(101, "Kim");
MyMap.put(104, "Jo");
MyMap.put(105, "Sam");
//printing the map
System.out.println("MyMap contains: " + MyMap);
//printing the first key in the map
System.out.println("The first key in the map is: " + MyMap.firstKey());
}
}
The output of the above code will be:
MyMap contains: {101=Kim, 102=John, 103=Marry, 104=Jo, 105=Sam}
The first key in the map is: 101
❮ Java.util - TreeMap
