TreeSet pollFirst() method in Java
The pollFirst() method of TreeSet in Java is used to retrieves and removes the first (lowest) element, or returns null if this TreeSet is empty.
Syntax:
E pollFirst()
Where, E is the type of elements maintained by this TreeSet container.
Parameters: This function does not accepts any parameter.
Return Type:It returns the first element of the Treeset if TreeSet is not empty else returns null.
Below programs illustrate the pollFirst() method in Java:
Example 1
import java.util.TreeSet;
public class GFG {
public static void main(String[] args)
{
TreeSet<Integer> ts = new TreeSet<Integer>();
ts.add( 0 );
ts.add( 1 );
ts.add( 2 );
ts.add( 3 );
ts.add( 4 );
ts.add( 5 );
ts.add( 6 );
System.out.println( "Before removing " +
"element from TreeSet: " + ts);
System.out.println( "First lowest element " +
"removed is : " + ts.pollFirst());
System.out.println( "After removing element" +
" from TreeSet: " + ts);
}
}
|
Output:
Before removing element from TreeSet: [0, 1, 2, 3, 4, 5, 6]
First lowest element removed is : 0
After removing element from TreeSet: [1, 2, 3, 4, 5, 6]
Example 2
import java.util.TreeSet;
public class GFG {
public static void main(String[] args)
{
TreeSet<String> ts = new TreeSet<String>();
System.out.println( "pollFirst() method when " +
"TreeSet is empty : " + ts.pollFirst());
ts.add( "Geeks" );
ts.add( "for" );
ts.add( "Geek" );
System.out.println( "Before removing element from" +
" TreeSet: " + ts);
System.out.println( "First lowest element removed is : "
+ ts.pollFirst());
System.out.println( "After removing element " +
"from TreeSet: " + ts);
}
}
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Output:
pollFirst() method when TreeSet is empty : null
Before removing element from TreeSet: [Geek, Geeks, for]
First lowest element removed is : Geek
After removing element from TreeSet: [Geeks, for]
If TreeSet is empty, then this method returns null.
Example 3
import java.util.TreeSet;
public class GFG {
public static void main(String[] args)
{
TreeSet<Integer> ts = new TreeSet<Integer>();
System.out.println( "Before removing " +
"element from TreeSet: " + ts);
System.out.println( "First lowest element " +
"removed is : " + ts.pollFirst());
System.out.println( "After removing element" +
" from TreeSet: " + ts);
}
}
|
Output:
Before removing element from TreeSet: []
First lowest element removed is : null
After removing element from TreeSet: []
Last Updated :
28 Dec, 2018
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