71 lines
2.0 KiB
Java
71 lines
2.0 KiB
Java
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// Java HashMap
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// Joe James 2023
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import java.util.Map;
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import java.util.HashMap;
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import java.util.Map.Entry;
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import java.util.stream.*;
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class MapFunctions {
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public static void main (String[] args) {
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// 1. Create a HashMap, add kv pairs
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Map<String, Integer> ages = new HashMap<String, Integer>();
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// OR, to initialize capaacity,
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// Map<String, Integer> ages = new HashMap<String, Integer>(100);
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ages.put("Avni",11);
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ages.put("Bing", 12);
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ages.put("Cassie", 13);
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ages.put("Devarshi", 14);
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System.out.println(ages);
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// 2. Get an item from the map
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String person = "Cassie";
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System.out.println(person + " : " + ages.get(person));
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System.out.println("Frank" + " : " + ages.getOrDefault("Frank", 0));
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// 3. Check for membership
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System.out.println("Contains key Avni?: " + ages.containsKey("Avni"));
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System.out.println("Contains value 23?: " + ages.containsValue(23));
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// 4. Remove an item from the map
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ages.remove("Bing");
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System.out.println(ages);
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ages.remove("Devarshi", 41);
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System.out.println(ages);
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// 5. Get count of items in map
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System.out.println("Num Items = " + ages.size());
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// 6. Remove all items from map
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ages.clear();
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System.out.println("Empty map? " + ages.isEmpty());
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ages.put("Elena", 15);
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ages.put("Frank", 16);
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System.out.println(ages);
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// 7. Conditional add & replace
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ages.putIfAbsent("George", 23);
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ages.putIfAbsent("Elena", 5);
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System.out.println(ages);
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ages.replace("George", 23, 17);
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ages.replace("George", 44, 55);
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System.out.println(ages);
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// 8. Get collection of Values
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System.out.println(ages.values());
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// 9. Iterate keys using enhanced for loop
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for (String key : ages.keySet()) {
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System.out.println(key + " : " + ages.get(key));
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}
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// 10. Iterate KV pairs using enhanced for loop
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for (Map.Entry<String, Integer> pair : ages.entrySet()) {
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System.out.println(pair.getKey() + " : " + pair.getValue());
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}
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// 11. Iterate KV pairs using Java 8 Stream API
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ages.entrySet().stream().forEach(pair -> System.out.println(pair.getKey() + " : " + pair.getValue()));
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}
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}
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