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Java Collection, TreeMap Exercises: Get a reverse order view of the keys contained in a given map

Java Collection, TreeMap Exercises: Exercise-10 with Solution

Write a Java program to get a reverse order view of the keys contained in a given map.

Sample Solution:-

Java Code:

import java.util.*;
import java.util.Map.Entry;  
public class Example10 {  
     public static void main(String args[]) {

  // Create a tree map
  TreeMap <String,String> tree_map1 = new TreeMap <String,String> ();

  // Put elements to the map 
  tree_map1.put("C2", "Red");
  tree_map1.put("C1", "Green");
  tree_map1.put("C4", "Black");
  tree_map1.put("C3", "White");

  System.out.println("Orginal TreeMap content: " + tree_map1);
  System.out.println("Reverse order view of the keys: " + tree_map1.descendingKeySet());
 }
}

Sample Output:

Orginal TreeMap content: {C1=Green, C2=Red, C3=White, C4=Black}        
Reverse order view of the keys: [C4, C3, C2, C1]

Java Code Editor:

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Java: Tips of the Day

Try and catch:

Java is excellent at catching errors, but it can only recover gracefully if you tell it what to do. The cascading hierarchy of attempting to perform an action in Java starts with try, falls back to catch, and ends with finally. Should the try clause fail, then catch is invoked, and in the end, there's always finally to perform some sensible action regardless of the results. Here's an example:

try {
        cmd = parser.parse(opt, args); 
       
        if(cmd.hasOption("help")) {
                HelpFormatter helper = new HelpFormatter();
                helper.printHelp("Hello ", opt);
                System.exit(0);
                }
        else {
                if(cmd.hasOption("shell") || cmd.hasOption("s")) {
                String target = cmd.getOptionValue("tgt");
                } // else
        } // fi
} catch (ParseException err) {
        System.out.println(err);
        System.exit(1);
        } //catch
        finally {
                new Hello().helloWorld(opt);
        } //finally
} //try

It's a robust system that attempts to avoid irrecoverable errors or, at least, to provide you with the option to give useful feedback to the user. Use it often, and your users will thank you!

Ref: https://red.ht/3EZc9OC