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TreeMap ceilingKey() in Java with Examples

The ceilingKey() function of TreeMap Class returns the least key greater than or equal to the given key or null if the such a key is absent.

Syntax:

`public K ceilingKey(K key)`

Parameters: This method accepts a mandatory parameter key which is the key to be searched for.

Return Value: This method returns the least key which is greater than or equal to the given key value.
If such a key is absent, null is returned.

Exceptions: This method throws following exceptions:

• ClassCastException – Thrown if the specified key can’t be compared with the given key values.
• NullPointerException – Thrown if the given key is null and the map uses natural ordering or the comparator does not permit null values.

Below are the examples to illustrate ceilingKey() method:

Program 1: To demonstrate use of ceilingKey() method for a TreeMap with comparator

 `import` `java.util.*;`` ` `public` `class` `Main {``    ``public` `static` `void` `main(String[] args)``    ``{`` ` `        ``// creating tree map``        ``NavigableMap``            ``treemap = ``new` `TreeMap((a, b)``                                              ``-> ((a > b)``                                                      ``? ``1``                                                      ``: ((a == b)``                                                             ``? ``0``                                                             ``: -``1``)));`` ` `        ``// populating tree map``        ``treemap.put(``1``, ``" A "``);``        ``treemap.put(``2``, ``" B "``);``        ``treemap.put(``3``, ``" C "``);``        ``treemap.put(``4``, ``" D "``);``        ``treemap.put(``6``, ``" E "``);``        ``try` `{``            ``System.out.println(``"Ceiling key entry for 5: "``                               ``+ treemap.ceilingKey(``5``));``        ``}``        ``catch` `(Exception e) {``            ``System.out.println(``"Exception: "` `+ e);``        ``}``    ``}``}`

Output:

```Ceiling key entry for 5: 6
```

Program 2: To demonstrate use of ceilingKey() method for a TreeMap without any comparator

 `import` `java.util.*;`` ` `public` `class` `Main {``    ``public` `static` `void` `main(String[] args)``    ``{`` ` `        ``// creating tree map``        ``NavigableMap``            ``treemap = ``new` `TreeMap();`` ` `        ``// populating tree map``        ``treemap.put(``1``, ``" A "``);``        ``treemap.put(``2``, ``" B "``);``        ``treemap.put(``3``, ``" C "``);``        ``treemap.put(``4``, ``" D "``);``        ``treemap.put(``6``, ``" E "``);``        ``treemap.put(``7``, ``" F "``);`` ` `        ``// Since 6 is the least value greater than 5,``        ``// it is returned as the key.``        ``System.out.println(``"Ceiling key entry for 5: "``                           ``+ treemap.ceilingKey(``5``));``    ``}``}`

Output:

```Ceiling key entry for 5: 6
```

Program 3: To demonstrate use of ceilingKey() method when it will return null

 `import` `java.util.*;`` ` `public` `class` `Main {``    ``public` `static` `void` `main(String[] args)``    ``{`` ` `        ``// creating tree map``        ``NavigableMap``            ``treemap = ``new` `TreeMap();`` ` `        ``// populating tree map``        ``treemap.put(``1``, ``" A "``);``        ``treemap.put(``2``, ``" B "``);``        ``treemap.put(``3``, ``" C "``);``        ``treemap.put(``4``, ``" E "``);``        ``treemap.put(``5``, ``" D "``);`` ` `        ``// Since 10 is not present in the Map``        ``// and neither any Key is present greater than 10``        ``// Hence this will return null``        ``System.out.println(``"Ceiling key entry for 10: "``                           ``+ treemap.ceilingKey(``10``));``    ``}``}`

Output:

```Ceiling key entry for 10: null
```

Program 4: To show NullPointerException

 `import` `java.util.*;`` ` `public` `class` `Main {``    ``public` `static` `void` `main(String[] args)``    ``{`` ` `        ``// creating tree map``        ``TreeMap``            ``treemap = ``new` `TreeMap();`` ` `        ``// populating tree map``        ``treemap.put(``2``, ``" two "``);``        ``treemap.put(``1``, ``" one "``);``        ``treemap.put(``3``, ``" three "``);``        ``treemap.put(``6``, ``" six "``);``        ``treemap.put(``5``, ``" five "``);`` ` `        ``try` `{``            ``// returns a NullPointerException``            ``// as key value can't be null``            ``// because of natural ordering``            ``System.out.println(``"Ceiling key entry for null value : "``                               ``+ treemap.ceilingKey(``null``));``        ``}``        ``catch` `(Exception e) {``            ``System.out.println(``"Exception: "` `+ e);``        ``}``    ``}``}`

Output:

```Exception: java.lang.NullPointerException
```

Program 5: To demonstrate ClassCastException

 `import` `java.util.*;`` ` `public` `class` `Main {``    ``public` `static` `void` `main(String[] args)``    ``{`` ` `        ``// creating tree map``        ``NavigableMap``            ``treemap = ``new` `TreeMap();`` ` `        ``// populating tree map``        ``treemap.put(``1``, ``" A "``);``        ``treemap.put(``2``, ``" B "``);``        ``treemap.put(``3``, ``" C "``);``        ``treemap.put(``4``, ``" E "``);``        ``treemap.put(``5``, ``" D "``);`` ` `        ``try` `{``            ``// returns ClassCastException``            ``// as we cannot compare a String object with an Integer object``            ``System.out.println(``"Ceiling key entry for \"asd\": "``                               ``+ treemap.ceilingKey(``new` `String(``"asd"``)));``        ``}``        ``catch` `(Exception e) {``            ``System.out.println(``"Exception: "` `+ e);``        ``}``    ``}``}`

Output:

```Exception: java.lang.ClassCastException:
java.lang.Integer cannot be cast to java.lang.String
```

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