Java 在线编译器

Main.java

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StdinOptional input fed to the program on stdin - one line per line.2 linesAlice 30

Output

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

public class Main {
    public static void main(String[] args) {
        Map<String, Integer> ages = new HashMap<>();
        ages.put("Alice", 30);
        ages.put("Bob", 25);
        ages.put("Carol", 35);

        System.out.println("Bob -> " + ages.get("Bob"));
        System.out.println("contains Carol: " + ages.containsKey("Carol"));
        System.out.println("Dave or default: " + ages.getOrDefault("Dave", -1));

        // getOrDefault makes frequency counting a one-liner
        String[] words = {"apple", "banana", "apple", "cherry", "apple"};
        Map<String, Integer> counts = new HashMap<>();
        for (String w : words) {
            counts.put(w, counts.getOrDefault(w, 0) + 1);
        }
        System.out.println("apple count: " + counts.get("apple"));

        ages.remove("Bob");
        System.out.println("size after remove: " + ages.size());

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