TreeMap floorKey() in Java with Examples - GeeksforGeeks

17 Sep, 2018
Pre-requisite: TreeMap in Java
The floorKey() method is used to return the greatest key less than or equal to given key from the parameter.
Syntax:
public K floorKey(K key)
Parameter: This method accepts a mandatory parameter key which is the key to be matched.
Return Value: The method call returns the greatest key less than or equal to key, or null if there is no such key.
Exception: This method throws following exceptions:
ClassCastException: When the specified key cannot be compared with the key available in Map.
NullPointerException: When the specified key in map is null and it uses naturalordering which means, comparator does not permit null keys.
Below are examples to illustrate the use of floorKey() method:
Example 1:
// Java program to demonstrate floorKey() method  import java.util.TreeMap;  public class FloorKeyDemo {    public static void main(String args[])    {          // create an empty TreeMap        TreeMap<Integer, String> numMap = new TreeMap<Integer, String>();          // Insert the values        numMap.put(6, "Six");        numMap.put(1, "One");        numMap.put(5, "Five");        numMap.put(3, "Three");        numMap.put(8, "Eight");        numMap.put(10, "Ten");          // Print the Values of TreeMap        System.out.println("TreeMap: " + numMap.toString());          // Get the greatest key mapping of the Map          // As here 11 is not available it returns 10        // because ten is less than 11        System.out.print("Floor Entry of Element 11 is: ");        System.out.println(numMap.floorKey(11));          // This will give null        System.out.print("Floor Entry of Element 0 is: ");        System.out.println(numMap.floorKey(0));    }}
TreeMap: {1=One, 3=Three, 5=Five, 6=Six, 8=Eight, 10=Ten}
Floor Entry of Element 11 is: 10
Floor Entry of Element 0 is: null

Example 2: To demonstrate NullPointerException
// Java program to demonstrate floorKey() method  import java.util.TreeMap;  public class FloorKeyDemo {    public static void main(String args[])    {          // create an empty TreeMap        TreeMap<Integer, String>            numMap = new TreeMap<Integer, String>();          // Insert the values        numMap.put(6, "Six");        numMap.put(1, "One");        numMap.put(5, "Five");        numMap.put(3, "Three");        numMap.put(8, "Eight");        numMap.put(10, "Ten");          // Print the Values of TreeMap        System.out.println("TreeMap: " + numMap.toString());          try {            // Passing null as parameter to floorKey()            // This will throw exception            System.out.println(numMap.floorKey(null));        }        catch (Exception e) {            System.out.println("Exception: " + e);        }    }}
TreeMap: {1=One, 3=Three, 5=Five, 6=Six, 8=Eight, 10=Ten}
Exception: java.lang.NullPointerException

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