Comparing Key items with an integer using Hasmap in Java

I'm trying to compare the Key item to see if is equal to the integer that is in the Translate constructor. But someone I can't really figure it out. Sorry for the mess and I' still fairly new to Java. Thanks

public class Translate {
    
        Map<Integer, String> map = new HashMap<>();
        private int number;

        map.put(0, "zero");
        map.put(1, "one");
        map.put(2, "two");
        map.put(3, "three");
        map.put(4, "four");
        map.put(5, "five");
        map.put(6, "six");
        map.put(7, "seven");
        map.put(8, "eight");
        map.put(9, "nine");
    
        public Translate(int number) {
            this.number = number;
        }
    
        //this is where I'm stuck. I need to compare the Key item to see if is it equal to the integer that is in the Translate constructor. 
        public String convertToString() {
            if (map.get(number) == this.number) {
            };
        }
    }

You have to try something like this:

import java.util.*;

public class Translate {
    
    private static Map<Integer, String> map;
    
    static {
        map = new HashMap<>();
        map.put(0, "zero");
        map.put(1, "one");
        map.put(2, "two");
        map.put(3, "three");
        map.put(4, "four");
        map.put(5, "five");
        map.put(6, "six");
        map.put(7, "seven");
        map.put(8, "eight");
        map.put(9, "nine");
    }
        
    private int number;
    
    public Translate(int number) {
        this.number = number;
    }
    
    public String convertToString() {
        if (map.containsKey(this.number)) {
            return map.get(this.number);
        }
        return null;
    }
    
    public static void main(String[] args) {
        Translate t = new Translate(7);
        System.out.println(t.convertToString());
    }
}

I'm not the expert on java but here is what i found troublesome

if (map.get(number).equals(this.number)) <--- 1.you are fetching the value not the key in this.

Instead check with map.contains() , if returned true by it, return the value of the key you passed.

2. You should never compare objects with "==" but should instead use .equals() method of that collection , if it is there.

PS: Open for feedback if I wrote something wrong

public String convertToString() {
  // You just need to see if the map contains this key, so you can use containsKey
  if (map.containsKey(this.number)) {
    // Do whatever else you want to do
  }
}

Alternatively, if you will use the value in the map if it exists, you can skip the containsKey and just go straight to get

public String convertToString() {
  // Return either the value in the map with key of this.number, or a message that 
  // indicates that no value is present
  return map.getOrDefault(this.number, "Couldn't find " + this.number + "!");
}

You should call Translate method with any value at first. Or, you can give default value to number, such as int number =5;

Then you can use

public String convertToString() {
    if (map.containsKey(this.number)) {
        return map.get(this.number);
    }
    return null;
} method.

Then, print the value System.out.println(t.convertToString());

Try this:

public class Translate {

    private int number;

    Map<Integer, String> map = Map.of(0, "zero", 1, "one", 2, "two", 3, "three", 4, "four", 5, "five", 6, "six", 7, "seven", 8, "eight", 9, "nine");

    public Translate(int number) {
        this.number = number;
    }

    public String convertToString() {
        return map.get(number);  // returns null if there's no entry
    }
}

Theabove code rerurns null if there's no entry for the number. Alternatively, you could just return the number itself.

public String convertToString() {
    return map.getOrDefault(number, Integer.toString(number));
}

If you wanted to be strict, you could throw an exception if an invalid number is passed to the constructor:

public Translate(int number) {
    if (!map.containsKey(number)) {
        throw new IllegalArgumentException("number must be 0-9");
    }
    this.number = number;
}