How to implement Java list to rank the specified element first

It can be implemented in the following ways:

1. Use List method to implement it

Method 1: Use add(0, element) and remove()

Gets the index of the specified element.

Removes the element from its current position.

Use the add(0, element) method to insert it into the first position.

Sample code:

import ;
import ;
 
public class Main {
    public static void main(String[] args) {
        List&lt;String&gt; list = new ArrayList&lt;&gt;();
        ("Alice");
        ("Bob");
        ("Charlie");
        ("David");
 
        ("Original List: " + list);
 
        // Specify the element to be ranked first        String element = "Charlie";
 
        // Get the index of the element        int index = (element);
        if (index != -1) {
            // Remove elements            (index);
            // Insert to the first position            (0, element);
        }
 
        ("Adjusted List: " + list);
    }
}

Running results:

Original list: [Alice, Bob, Charlie, David]
Adjusted list: [Charlie, Alice, Bob, David]

Method 2: Use ()

If you only need to swap the location of the specified element and the first element, you can use the () method.

Sample code:

import ;
import ;
import ;
 
public class Main {
    public static void main(String[] args) {
        List&lt;String&gt; list = new ArrayList&lt;&gt;();
        ("Alice");
        ("Bob");
        ("Charlie");
        ("David");
 
        ("Original List: " + list);
 
        // Specify the element to be ranked first        String element = "Charlie";
 
        // Get the index of the element        int index = (element);
        if (index != -1) {
            // Swap elements            (list, 0, index);
        }
 
        ("Adjusted List: " + list);
    }
}

Running results:

Original list: [Alice, Bob, Charlie, David]
Adjusted list: [Charlie, Bob, Alice, David]

2. Custom sorting

If the requirements are more complex, you can use Comparator to customize the sorting logic.

Sample code:

import ;
import ;
import ;
import ;
 
public class Main {
    public static void main(String[] args) {
        List&lt;String&gt; list = new ArrayList&lt;&gt;();
        ("Alice");
        ("Bob");
        ("Charlie");
        ("David");
 
        ("Original List: " + list);
 
        // Specify the element to be ranked first        final String element = "Charlie";
 
        // Custom sorting        (list, new Comparator&lt;String&gt;() {
            @Override
            public int compare(String o1, String o2) {
                if ((element)) {
                    return -1;
                } else if ((element)) {
                    return 1;
                } else {
                    return 0;
                }
            }
        });
 
        ("Adjusted List: " + list);
    }
}

Running results:

Original list: [Alice, Bob, Charlie, David]
Adjusted list: [Charlie, Alice, Bob, David]

3. Things to note

If the specified element does not exist in the list, the indexOf() method will return -1, and corresponding error processing is required.

If there are multiple identical elements in the list, the indexOf() method will only move the first matching element.

When operating lists in multi-threaded environments, you need to pay attention to thread safety issues.

With the above method, you can easily move the specified element to the first position of the List.

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