- Java.util Package Classes
- Java.util - Home
- Java.util - ArrayDeque
- Java.util - ArrayList
- Java.util - Arrays
- Java.util - BitSet
- Java.util - Calendar
- Java.util - Collections
- Java.util - Currency
- Java.util - Date
- Java.util - Dictionary
- Java.util - EnumMap
- Java.util - EnumSet
- Java.util - Formatter
- Java.util - GregorianCalendar
- Java.util - HashMap
- Java.util - HashSet
- Java.util - Hashtable
- Java.util - IdentityHashMap
- Java.util - LinkedHashMap
- Java.util - LinkedHashSet
- Java.util - LinkedList
- Java.util - ListResourceBundle
- Java.util - Locale
- Java.util - Observable
- Java.util - PriorityQueue
- Java.util - Properties
- Java.util - PropertyPermission
- Java.util - PropertyResourceBundle
- Java.util - Random
- Java.util - ResourceBundle
- Java.util - ResourceBundle.Control
- Java.util - Scanner
- Java.util - ServiceLoader
- Java.util - SimpleTimeZone
- Java.util - Stack
- Java.util - StringTokenizer
- Java.util - Timer
- Java.util - TimerTask
- Java.util - TimeZone
- Java.util - TreeMap
- Java.util - TreeSet
- Java.util - UUID
- Java.util - Vector
- Java.util - WeakHashMap
- Java.util Package Extras
- Java.util - Interfaces
- Java.util - Exceptions
- Java.util - Enumerations
- Java.util Useful Resources
- Java.util - Useful Resources
- Java.util - Discussion
Java TreeMap firstEntry() Method
Description
The Java TreeMap firstEntry() method is used to return a key-value mapping associated with the least key in this map, or null if the map is empty.
Declaration
Following is the declaration for java.util.TreeMap.firstEntry() method.
public Map.Entry<K,V> firstEntry()
Parameters
NA
Return Value
The method call returns an entry with the least key, or null if this map is empty.
Exception
NA
Getting First Mapping from the TreeMap of Integer,Integer Pairs Example
The following example shows the usage of Java TreeMap firstEntry() method to get the first mapping in the treemap object. We've created a TreeMap object of Integer,Integer pairs. Then few entries are added to map and using firstEntry() we've retrieved the first mapping and then printed the same.
package com.tutorialspoint; import java.util.TreeMap; public class TreeMapDemo { public static void main(String[] args) { // creating tree map TreeMap<Integer, Integer> treemap = new TreeMap<>(); // populating tree map treemap.put(2, 2); treemap.put(1, 1); treemap.put(3, 3); treemap.put(6, 6); treemap.put(5, 5); System.out.println("Checking first entry"); System.out.println("First entry is: "+ treemap.firstEntry()); } }
Output
Let us compile and run the above program, this will produce the following result.
Checking first entry First entry is: 1=1
Getting First Mapping from the TreeMap of Integer,String Pairs Example
The following example shows the usage of Java TreeMap firstEntry() method to get the first mapping in the treemap object. We've created a TreeMap object of Integer,String pairs. Then few entries are added to map and using firstEntry() we've retrieved the first mapping and then printed the same.
package com.tutorialspoint; import java.util.TreeMap; public class TreeMapDemo { public static void main(String[] args) { // creating tree map TreeMap<Integer, String> 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"); System.out.println("Checking first entry"); System.out.println("First entry is: "+ treemap.firstEntry()); } }
Output
Let us compile and run the above program, this will produce the following result.
Checking first entry First entry is: 1=one
Getting First Mapping from the TreeMap of Integer,Object Pairs Example
The following example shows the usage of Java TreeMap firstEntry() method to get the first mapping in the treemap object. We've created a TreeMap object of Integer,Student pairs. Then few entries are added to map and using firstEntry() we've retrieved the first mapping and then printed the same.
package com.tutorialspoint; import java.util.TreeMap; public class TreeMapDemo { public static void main(String[] args) { // creating tree map TreeMap<Integer, Student> treemap = new TreeMap<>(); // populating tree map treemap.put(2, new Student(2, "Robert")); treemap.put(1, new Student(1, "Julie")); treemap.put(3, new Student(3, "Adam")); treemap.put(6, new Student(6, "Julia")); treemap.put(5, new Student(5, "Tom")); System.out.println("Checking first entry"); System.out.println("First entry is: "+ treemap.firstEntry()); } } class Student { int rollNo; String name; Student(int rollNo, String name){ this.rollNo = rollNo; this.name = name; } @Override public String toString() { return "[ " + this.rollNo + ", " + this.name + " ]"; } @Override public boolean equals(Object obj) { if(obj == null) return false; Student s = (Student)obj; return this.rollNo == s.rollNo && this.name.equalsIgnoreCase(s.name); } }
Output
Let us compile and run the above program, this will produce the following result.
Checking first entry First entry is: 1=[ 1, Julie ]
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