Iterating over Map implementations requires selecting appropriate strategies based on whether you need keys, values, or both, alongside considerations for concurrent modification and Java version compatibility.

Entry-Based Traversal

Accessing both keys and values simultaneously through entrySet() offers optimal performance by avoiding repeated hash loookups:

Map<Long, String> sessionCache = new HashMap<>();
sessionCache.put(1001L, "Active");
sessionCache.put(1002L, "Pending");
sessionCache.put(1003L, "Closed");

for (Map.Entry<Long, String> record : sessionCache.entrySet()) {
    Long sessionId = record.getKey();
    String status = record.getValue();
    System.out.printf("Session %d: %s%n", sessionId, status);
}

Key or Value Isolation

When only identifiers or data elements are required, iterate over specific collections:

// Process only keys
for (Long id : sessionCache.keySet()) {
    auditLog.append("Scanned ID: ").append(id).append("\n");
}

// Aggregate values
for (String state : sessionCache.values()) {
    if ("Active".equals(state)) {
        activeCounter.increment();
    }
}

Iterator-Based Navigation

Explicit Iterator instances enable safe element removal during traversal:

Iterator<Map.Entry<Long, String>> cursor = sessionCache.entrySet().iterator();
while (cursor.hasNext()) {
    Map.Entry<Long, String> entry = cursor.next();
    if ("Closed".equals(entry.getValue())) {
        cursor.remove(); // Safe deletion
    }
}

Functional Approach (Java 8+)

Lambda expressions provide concise syntax for read-only operations:

sessionCache.forEach((id, status) -> {
    if (status.startsWith("A")) {
        notificationService.alert(id);
    }
});