WeakHashMap Class in Java

// Java Program to Illustrate WeakHashMap class
// Via close(), containsValue(), containsKey()
// and isEmpty() method

// Importing required classes
import java.util.Map;
import java.util.WeakHashMap;

// Main class
// WeakHashMapdemo
class GFG {

    // Main driver method
    public static void main(String[] arg)
    {

        // Creating an empty WeakHashMap
        // of Number and string type
        Map<Number, String> weak
            = new WeakHashMap<Number, String>();

        // Inserting custom elements
        // using put() method
        weak.put(1, "geeks");
        weak.put(2, "for");
        weak.put(3, "geeks");

        // Printing and alongside checking weak map
        System.out.println("our weak map: " + weak);

        // Checking if "for" exist
        if (weak.containsValue("for"))
            System.out.println("for exist");

        // Checking if 1 exist as a key in Map
        if (weak.containsKey(1))
            System.out.println("1 exist");

        // Removing all data
        // using clear() method
        weak.clear();

        // Checking whether the Map is empty or not
        // using isEmpty() method
        if (weak.isEmpty())

            // Display message for better readability
            System.out.println("empty map: " + weak);
    }
}

// Java Program to Illustrate WeakHashMap class
// Via entrySet(), keySet() and Values() Method

// Importing required classes
import java.util.Collection;
import java.util.Map;
import java.util.Set;
import java.util.WeakHashMap;

// Main class
// WeakHashMapdemo
class GFG {

    // Main driver method
    public static void main(String[] arg)
    {

        // Creating an empty WeakHashMap
        // of number and string type
        Map<Number, String> weak
            = new WeakHashMap<Number, String>();

        // Inserting elements
        // using put() method
        weak.put(1, "geeks");
        weak.put(2, "for");
        weak.put(3, "geeks");

        // Creating object of Set interface
        Set set1 = weak.entrySet();

        // Checking above Set
        System.out.println(set1);

        // Creating set for key
        Set keySet = weak.keySet();

        // Checking keySet
        System.out.println("key set: " + keySet);

        Collection value = weak.values();

        // Checking values of map and printing them
        System.out.println("values: " + value);
    }
}

// Java code remove(), putAll()
// get() and size() method

import java.util.Collection;
import java.util.Map;
import java.util.Set;
import java.util.WeakHashMap;

class WeakHashMapdemo {
    public static void main(String[] arg)
    {
        Map<Number, String> weak
            = new WeakHashMap<Number, String>();
        weak.put(1, "geeks");
        weak.put(2, "for");
        weak.put(3, "geeks");

        Map<Number, String> weak1
            = new WeakHashMap<Number, String>();
        weak1.putAll(weak);

        // Getting value of key 2
        System.out.println(weak1.get(2));

        // Printing the size of map
        // using size() method
        System.out.println("Size of map is: "
                           + weak1.size());

        // Removing second element
        // using standard remove() method
        weak1.remove(2);

        // Printing the size after removing key and value
        // pair
        System.out.println("Size after removing: "
                           + weak1.size());
    }
}