Java Print Invertedtriangle Java9 Private Interface Methods String Compare Java Hashmap Entryset String Uppercase Java Bytearrayinputstream Thread Interrupt Java8 Functional Interfaces Collection Size Java9 Collection Factory Methods Java String Comparetoignorecase Collection Print Java String Split Method Break Java Print Parallelogram Method Varargs1 Data Replace Collection Rotate Number Todegrees Java Hashmap Getorindex Net Port Dir Hidden Dir Search File Java8 Lambda Expressions Java String Tolowercase Java Character Java Hashmap Clone Dir Create String Replace Java Arraylist Size Java Modifier Types Method For Java Arraylist Toarray Java Arraylist Contains Java String Compareto Env Version Java8 Datetime Api Java Hashmap Thread Deadlock Data_Linklist Exception Overloaded Method Number Exp Java Hashmap Merge File Rename Arrays Find Java8 Base64 Java8 Streams Java Examples Java Arraylist Ensurecapacity Dir Sub Java Hashmap Clear Java String Replaceall Java Hashmap Putifabsent Exception Chain File Read Number Xxxvalue Java Arraylist Indexof Arrays Compare Thread Status Java Override Overload Java Hashmap Computeifabsent Data Search Character Tostring Thread Priorityinfo Character Tolowercase Java Url Processing Number Parseint Java Dictionary Class Java Object Wait Java Data Structures Java Arraylist Set File Delete Java Date Time Collection Sublist Java Hashtable Class String Concatenation Java Stack Class Java String Startswith Java Scanner Class Java String Contains Data Insert Env Classpath Java String Getbytes Java Filewriter Java Mysql Connect Java Serialization File Dir Net Webpage Character Iswhitespace Dir Traverse Java String Touppercase Java Methods Exception Hierarchy Thread Id Date Time Am Pm Arrays Upperbound Java If Else Switch Java9 Improved Javadocs File Compare Date Year Month Data Swap Java Switch Case File Copy Character Isletter Method Fibonacci Java Hashmap Putall Java String Tochararray Java Object Getclass Java String Getchars Arrays Fill Number Atan2 Collection Reverse Java Hashmap Size Java Sending Email Exception Printstack Thread Alive Exception Finally Java Object Clone Number Random Java Arraylist Lastindexof Java Hashmap Get Number Equals Collection Remove Java String Concat Method Tower Java9 Multiresolution Image_Api Thread Showall Java Hashmap Isempty Number Ceil Java Object Classes File Create Java Basic Syntax Java Arraylist Removerange Java8 Nashorn Javascript Java String Tostring Collection Iterator Arrays Union Java Object Finalize Java9 Multirelease Jar Java Print The Triangle Data Intopost Java String Valueof Arrays Equal Character Touppercase Net Address Arrays Remove Exception Catch File Write Method Override Net Serverfile Java Exceptions Java Applet Basics Java Print Diamond Java Arraylist String Removing Char Java Number Java Hashmap Foreach Java Bitset Class Java9 Inner Class Diamond Operator Method Enum Java Vector Class Java String Equalsignorecase Java Arraylist Tostring Java9 Completablefuture Api Improvements Java String Replacefirst Java Iterator Net Urldate Java String Equals Java Hashmap Values Java Arraylist Containsall Java Inheritance Arrays Output Java String Substring Number Rint Exception Thread Java Stringbuffer Java String Contentequals Number Tostring Java File Java String Copyvalueof Data Element Number Floor Java Object Notify Dir Empty Java Enumeration Interface Java Print Rect Method Label Dir Delete Java Hashtable Class Method Array Java Object Tostring Java Enum Java String Isempty File Date Modify Java String Regionmatches Character Islowercase Java Interfaces Java Arraylist Remove File Size Collection Replace Thread Monitor File Exist Arrays_Merge Collection Iterate Number Valueof Exception Method Java Properties Class Java Hashmap Remove String Search Java Package Thread Suspend File Create Temp Dir Current Java Files Io Java Inner Class Java Arraylist Clone Java Hashmap Replaceall Dir Search Java Datainputstream Collection Hashtable Key Java Arraylist Trimtosize Java Networking Java Object Wait Timeout Nanos Java Loop Java Object Class Dir Modification Java Object Hashcode Number Abs Data Stack Number Asin Collection Shuffle Collection Compare Java Anonymous Class Java Arraylist Sublist Java8 Optional Class Java Hashmap Containsvalue Data Add Java Environment Setup Dir Hierarchy Java Arraylist Foreach Java9 Process Api Improvements Number Cos Java Documentation String Split Java String Endswith Character Isdigit Collection All Arrays Search Number Atan Dir Display Net Url Header Method Continue String Optimization Java Bytearrayoutputstream Number Max Java String Trim Number Min Java Arraylist Isempty Java String Charat Java Dataoutputstream Java Regular Expressions Java String Subsequence Data Queue Java Arraylist Replaceall String Format Java Map Interface Arrays Insert Net Filetime Java String Hashcode Java String Length Collection Minmax Method Factorial Dir Parent Number Sqrt Arrays Extension Java Arraylist Clear Java8 Method References Java String Intern Number Compareto Java Linkedlist Java Collections Method Overloading Java9 New Features Java Hashmap Containskey Net Url Net Connected Date Time Datetime Java9 Optional Class Improvements Net Localip Method Varargs Env Compile Net Multisoc Java Filereader Java String Number Tan String Reverse Java Arraylist Removeif Java Array Thread Procon Java Polymorphism Java Arraylist Sort Java Arraylist Add Java Print Multiplicationtable Collection Enumeration Env Run Java8 Default Methods Java String Matches Collection Conversion Java String Lastindexof Java9 Repl Java9 Module System Net Serversocket Socket Character Isuppercase Java Hashmap Put Java Arraylist Get Java Arraylist Addall Java Variable Types Number Pow Data Update Collection Readonly Date Timestamp2Date Data Reverse Thread Stop Java Object Wait Timeout Java Hashmap Replace Arrays Removeall Java Hashset Java Abstraction Java Operators Java Arraylist Retainall Thread Getpri Exception User Method Enum1 File Read Only Java Hashmap Computeifpresent Data Vecsort Java Object Notifyall Java Generics Java Hashmap Keyset Dir Root Java Hashmap Compute Dir Size Number Round Arrays Reverse Java Arraylist Removeall Java Basic Datatypes Arrays Retainall Java9 Try With Resources Improvement Java Arraylist Surecapacity Java Tutorial Thread Name Number Toradians Java Multithreading Number Sin Java Encapsulation Java8 New Features Data Vec Max String Regionmatch Java Stringtokenizer Example Java9 Enhanced Deprecated Annotation Arrays Min Max Number Log File Date File Append Method Instanceof Java9 Stream Api Improvements String Last Occurance Java String Replace Number Acos Java Intro Java String Indexof Number Parseint Java Object Equals Collection Array String Performance

hashmap.putIfAbsent(K key, V value)

import java.util.HashMap;

class Main {
    public static void main(String[] args) {
        // Create a HashMap
        HashMap&lt;Integer, String> sites = new HashMap<>();

        // Add some elements to the HashMap
        sites.put(1, "Google");
        sites.put(2, "tutorialpro");
        sites.put(3, "Taobao");
        System.out.println("sites HashMap: " + sites);

        // Key does not exist in the HashMap
        sites.putIfAbsent(4, "Weibo");

        // Key exists in the HashMap
        sites.putIfAbsent(2, "Wiki");
        System.out.println("Updated sites HashMap: " + sites);
    }
}

sites HashMap: {1=Google, 2=tutorialpro, 3=Taobao}
Updated sites HashMap: {1=Google, 2=tutorialpro, 3=Taobao, 4=Weibo}

sites.putIfAbsent(2, "Wiki");