הגדר ומפה

import java.util.HashSet;
import java.util.Set;

Set<String> uniqueNames = new HashSet<>();
uniqueNames.add("Alice");
uniqueNames.add("Bob");
uniqueNames.add("Alice"); // This insertion will be ignored since "Alice" is already present

System.out.println(uniqueNames.size()); // Prints 2

import java.util.HashMap;
import java.util.Map;

Map<String, Integer> ageMap = new HashMap<>();
// Insert or update key-value pairs
ageMap.put("Alice", 25);
ageMap.put("Bob", 30);

// Retrieve value by key
int aliceAge = ageMap.get("Alice"); // Returns 25

// Verify if a key or value exists
boolean hasBob = ageMap.containsKey("Bob"); // Returns true

for (Map.Entry<String, Integer> entry : ageMap.entrySet()) {
    System.out.println(entry.getKey() + " is " + entry.getValue() + " years old.");
}