Map.containsKey(Object): If this map permits null values, then a return value of Before going into that demonstration, I will first point out that the Javadoc documentation for Map.get(Object) does explicitly warn about the subtle differences between ![]() In this blog post, I demonstrate these aspects of Null from a "get" call should consistently match a "false" return from the "containsKey" method. Null on a get call for that same key, then it is likely that the key maps to aĬontainsKey(Object) while at the same time returning " Often this doesn't matter, but if it does, one can use Map.containsKey() to determine if the Map to return its value for the given key, but that value might be a null. Map implementation allows for null values, then it is possible for the A common assumption might be made that a null returned from Map.get(Object) indicates there is no entry with the provided key in the map, but this is not always the case. Map's get(Object) method and to react differently based on whether the value returned is null or not. * This example uses containsKey() method to search for a key in HashMap.When using Java's Map implementations, it is sometimes common to invoke the * Java Program to to check if a key exists in HashMap or not. Accordingly, our program will print whether a given key exists in the HashMap or not. If the key exists then this method will return true otherwise it will return false. Our program reads input from the command prompt using the Scanner class and uses containsKey() to check if a given key exists or not. Later, I have asked the user to enter a key in the command prompt, which you can check against this HashMap. In this example, we have first created a HashMap with values using the double brace initialization technique, it's an anti-pattern but you can use it if your Map is not too big. Here is our sample program to demonstrate how you can use the containsKey() method to check if a given key exists in HashMap or not. How to check if a given key exists in HashMap in Java I also suggest all programmers go through a comprehensive book or course like The Complete Java Masterclass on Udemy to fill the gaps in your learning because Java is vast and there is always a better way to do things. This benefit of testing exposure really helps when you put your code into production. The biggest advantage of using an API method is that it has already been tried and tested by many programmers and faced many inputs and conditions which is impossible for your own code to execute. The great Java programmer Joshua Bloch even included a chapter on this on his all-time great Java book Effective Java, a must-read book for any Java programmer. That's why it's always better to write extensive JUnit tests for your code to test positive, negative, and boundary conditions.Īnother suggestion I want to make is that it's always better to use an API method if it can do the job, not just me but many greats have also advised this. Many Java programmers will test this code for some valid input and think that it's working fine, only to create a subtle bug in production. This code is fragile, it will not work if you have added null values into HashMap because HashMap does allow null values. This is supposed to be easy, right? Yes, it is easy if you know JDK API well, all you need to is call the containsKey() method, it returns true if the given key exists in HashMap, otherwise false but I have seen many programmers write code like below which is not correct, which inspired me to write this blog post. Hello Java programmers, if you have working in Java programming language or writing server side programs then you may know that one of the common programming tasks while using HashMap in Java is to check if a given key exists in the map or not.
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