从LinkedHashSet获取第一个元素的Java程序

// Java Program to Get the First Element from LinkedHashSet
// by converting it to an array or List
// Array is demonstrated below so do with List
// Importing generic java packages
import java.io.*;
import java.lang.*;
import java.util.*;
// Class
public class GFG {
    // Main driver method
    public static void main(String[] args)
        throws java.lang.Exception
    {
        // Creating a LinkedHashMap object
        // Declaring object of Integer type
        LinkedHashSet<Integer> hashSet
            = new LinkedHashSet<Integer>();
        // Adding elements to LinkedHashMap
        hashSet.add(2);
        hashSet.add(1);
        hashSet.add(4);
        hashSet.add(6);
        hashSet.add(8);
        // Condition check using isEmpty() method which
        // holds
        // True till there is a single element in an object
        // is remaining False, when there is no object left
        // or if initially there was no element added
        if (!hashSet.isEmpty()) {
            // Converting the above Map to an array
            Integer arr[] = new Integer[hashSet.size()];
            arr = hashSet.toArray(arr);
            // Accessing the first element by passing 0
            // as an argument which by default
            // accesses and prints out first element
            System.out.println("First element: " + arr[0]);
        }
    }
}


First element: 2


// Java Program to Get the First Element from LinkedHashSet
// Using Iterators
// Importing generic java packages
import java.util.*;
import java.lang.*;
import java.io.*;
// Class
public class GFG {
    // Main driver method
    public static void main(String[] args)
        throws java.lang.Exception
    {
        // Creating a LinkedHashMap
        LinkedHashSet<Integer> hashSet
            = new LinkedHashSet<Integer>();
        // Adding elements to LinkedHashMap
        hashSet.add(1);
        hashSet.add(2);
        hashSet.add(3);
        hashSet.add(4);
        hashSet.add(5);
        // Iterator over LinkedHashMap
        Iterator<Integer> iter = hashSet.iterator();
        if (iter != null && iter.hasNext()) {
            // Display the first element of Map using next()
            // ethod
            System.out.println(
                "First element in LinkedHashSet: "
                + iter.next());
        }
    }
}


First element in LinkedHashSet: 1


// Java Program to Get the First Element from LinkedHashSet
// Using Streams
// Importing generic java packages
import java.util.*;
import java.lang.*;
import java.io.*;
// Class
class GFG {
    // Main driver method
    public static void main(String[] args) throws java.lang.Exception
    {
        // Creating a LinkedHashMap
        LinkedHashSet<Integer> hashSet
            = new LinkedHashSet<Integer>();
        // Adding elemens to LinkedHashMap
        hashSet.add(1);
        hashSet.add(2);
        hashSet.add(3);
        hashSet.add(4);
        hashSet.add(5);
        // Checking whether Map is empty or not
        if (hashSet.size() == 0)
            // Display message
            System.out.println("The Set is Empty!");
        else {
            // Using stream() through findFirst() method
            // over the elements of LinkedHashMap
            int first = hashSet.stream().findFirst().get();
            // Printing the first element of LinkedHashMap
            System.out.println(
                "First element in LinkedHashSet: " + first);
        }
    }
}


First element in LinkedHashSet: 1