What is the entrySet() method in Java?
The HashMap class provides the java.util.HashMap.entrySet() method in Java. It is used to create and then return a ‘set’ of the same elements that are already present in the HashMap. It can be used with a loop to iterate over all the entries of a HashMap.Method Header
The header of the entrySet() method is given below. It returns the set view of all entries containing key-value pairs. To use it in our code we need to import java.util.HashMap package.
public Set<Map.Entry<key, value>> entrySet()
Parameters
The entrySet() method does not take any parameters.Return Type
The java.util.HashMap.entrySet() method returns an instance of the class set.
Example
import java.util.HashMap;
public class Driver1 {
public static void main(String[] args) {
// declare a custom hash map
HashMap<Integer, String> hashMap = new HashMap<Integer, String>();
// add data to the hash map
hashMap.put(1, "Monday");
hashMap.put(2, "Tuesday");
hashMap.put(3, "Wednesday");
hashMap.put(4, "Thursday");
hashMap.put(5, "Friday");
hashMap.put(6, "Saturday");
hashMap.put(7, "Sunday");
// print the original hash map
System.out.println("Original HashMap: " + hashMap + '\n');
// print the entrySet of the hash map
System.out.println("HashMap.entrySet(): " + hashMap.entrySet() + '\n');
// Try adding null value in the hash map
hashMap.put(0, null);
System.out.println("hashMap.put(0, null)");
System.out.println("HashMap.entrySet(): " + hashMap.entrySet() + '\n');
// Try adding null key and value pair to the hash map
hashMap.put(null, null);
System.out.println("hashMap.put(null, null)");
System.out.println("HashMap.entrySet(): " + hashMap.entrySet() + '\n');
// Try adding a null character as a value in the hash map
hashMap.put(null, "\0");
System.out.println("hashMap.put(null, \"\\0\")");
System.out.println("HashMap.entrySet(): " + hashMap.entrySet() + '\n');
}
}
Output
Original HashMap: {1=Monday, 2=Tuesday, 3=Wednesday, 4=Thursday, 5=Friday, 6=Saturday, 7=Sunday}
HashMap.entrySet(): [1=Monday, 2=Tuesday, 3=Wednesday, 4=Thursday, 5=Friday, 6=Saturday, 7=Sunday]
hashMap.put(0, null)
HashMap.entrySet(): [0=null, 1=Monday, 2=Tuesday, 3=Wednesday, 4=Thursday, 5=Friday, 6=Saturday, 7=Sunday]
hashMap.put(null, null)
HashMap.entrySet(): [0=null, null=null, 1=Monday, 2=Tuesday, 3=Wednesday, 4=Thursday, 5=Friday, 6=Saturday, 7=Sunday]
hashMap.put(null, "\0")
HashMap.entrySet(): [0=null, null= , 1=Monday, 2=Tuesday, 3=Wednesday, 4=Thursday, 5=Friday, 6=Saturday, 7=Sunday]
Explanation
In the code snippet above, we have first of all imported the java.util.HashMap package. It allows us to use the HashMap and entrySet() method. We then create a hashMap which is the object of the HashMap class. Our hashMap contains strings as values. The keys are integers. We then fill the hashMap. There are seven entries in total. We then use the setEntry() method to return a set view and then print in on the console.
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