HashMap

title: HashMap in Java description: HashMap - key-value store

Key-Value pairs store karna. No order guarantee, one null key allowed.

Create karna

java exampleWoHoTech

HashMap<String, Integer> map = new HashMap<>();
HashMap<String, Integer> map2 = new HashMap<>(16, 0.75f);

Basic Operations

java exampleWoHoTech

HashMap<String, Integer> marks = new HashMap<>();

// Put
marks.put("Ram", 85);
marks.put("Shyam", 92);
marks.put("Geeta", 78);
marks.put("Ram", 90);  // Existing key → value update hogi

// Get
marks.get("Ram");                      // 90
marks.getOrDefault("Mohan", 0);       // 0 (key nahi hai)

// Check
marks.containsKey("Ram");             // true
marks.containsValue(92);              // true
marks.size();                          // 3
marks.isEmpty();

// Remove
marks.remove("Geeta");
marks.remove("Ram", 85);              // Remove only if value matches

// Iteration
for (String key : marks.keySet()) System.out.println(key + ": " + marks.get(key));
for (Map.Entry<String, Integer> entry : marks.entrySet()) {
    System.out.println(entry.getKey() + " = " + entry.getValue());
}
marks.forEach((k, v) -> System.out.println(k + " = " + v));

// Keys and Values
Set<String> keys = marks.keySet();
Collection<Integer> values = marks.values();

// putIfAbsent
marks.putIfAbsent("Mohan", 75);  // Only adds if key doesn't exist

// getOrDefault
int score = marks.getOrDefault("Unknown", -1);

// compute
marks.compute("Ram", (k, v) -> v == null ? 1 : v + 1);
marks.computeIfAbsent("New", k -> 0);
marks.computeIfPresent("Ram", (k, v) -> v * 2);

// merge
marks.merge("Ram", 5, Integer::sum); // Add 5 to existing value

Word Frequency Count

String text = "java python java c++ python java"; Map<String, Integer> freq = new HashMap<>(); for (String word : text.split(" ")) freq.merge(word, 1, Integer::sum); freq.forEach((k, v) -> System.out.println(k + ": " + v));

title: HashMap in Java description: HashMap - key-value store

Key-Value pairs store karna. No order guarantee, one null key allowed.

Create karna

java exampleWoHoTech

HashMap<String, Integer> map = new HashMap<>();
HashMap<String, Integer> map2 = new HashMap<>(16, 0.75f);

Basic Operations

java exampleWoHoTech

HashMap<String, Integer> marks = new HashMap<>();

// Put
marks.put("Ram", 85);
marks.put("Shyam", 92);
marks.put("Geeta", 78);
marks.put("Ram", 90);  // Existing key → value update hogi

// Get
marks.get("Ram");                      // 90
marks.getOrDefault("Mohan", 0);       // 0 (key nahi hai)

// Check
marks.containsKey("Ram");             // true
marks.containsValue(92);              // true
marks.size();                          // 3
marks.isEmpty();

// Remove
marks.remove("Geeta");
marks.remove("Ram", 85);              // Remove only if value matches

// Iteration
for (String key : marks.keySet()) System.out.println(key + ": " + marks.get(key));
for (Map.Entry<String, Integer> entry : marks.entrySet()) {
    System.out.println(entry.getKey() + " = " + entry.getValue());
}
marks.forEach((k, v) -> System.out.println(k + " = " + v));

// Keys and Values
Set<String> keys = marks.keySet();
Collection<Integer> values = marks.values();

// putIfAbsent
marks.putIfAbsent("Mohan", 75);  // Only adds if key doesn't exist

// getOrDefault
int score = marks.getOrDefault("Unknown", -1);

// compute
marks.compute("Ram", (k, v) -> v == null ? 1 : v + 1);
marks.computeIfAbsent("New", k -> 0);
marks.computeIfPresent("Ram", (k, v) -> v * 2);

// merge
marks.merge("Ram", 5, Integer::sum); // Add 5 to existing value

HashMap

Create karna

Basic Operations

Word Frequency Count

Continue learning this concept

HashMap

Create karna

Basic Operations

Word Frequency Count

Continue learning this concept