Quiz

Java Intermediate

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Quiz

Question 1

Examine the following code snippet:

import java.util.HashMap;

public class Test {
    public static void main(String[] args) {
        HashMap<String, Integer> map = new HashMap<>();
        map.put("Alice", 85);
        map.put("Bob", 90);
        map.put("Alice", 95);
        System.out.println(map.get("Alice"));
    }
}

What is the output?

null

Question 2

What is the main difference between a HashMap and a LinkedHashMap?

LinkedHashMap maintains insertion order; HashMap does not.

HashMap maintains insertion order; LinkedHashMap does not.

HashMap is sorted by keys; LinkedHashMap is not.

LinkedHashMap does not allow null values; HashMap does.

Question 3

Examine the following code snippet:

import java.util.TreeMap;

public class Test {
    public static void main(String[] args) {
        TreeMap<Integer, String> map = new TreeMap<>();
        map.put(3, "C");
        map.put(1, "A");
        map.put(2, "B");
        System.out.println(map);
    }
}

What is the output?

{3=C, 1=A, 2=B}

{2=B, 1=A, 3=C}

{1=A, 2=B, 3=C}

The order is undefined.

Question 4

Examine the following code snippet that demonstrates bulk operations on a HashMap:

import java.util.HashMap;

public class Test {
    public static void main(String[] args) {
        HashMap<String, Integer> map1 = new HashMap<>();
        map1.put("A", 1);
        map1.put("B", 2);
        
        HashMap<String, Integer> map2 = new HashMap<>();
        map2.put("C", 3);
        map2.put("D", 4);
        
        map1.putAll(map2);
        System.out.println(map1);
        map1.clear();
        System.out.println("Map1 after clearing: " + map1);
    }
}

What is the expected behavior of this code?

Only map2 will be printed.

The maps will be merged, and then map1 will be empty after calling clear().

An exception will be thrown during the merge.

The maps remain unchanged.

.....

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