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Java Iterator

Theory

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Java Iterator

Iterator belongs to the Collections story. List = ordered, duplicates OK (ArrayList). Set = unique (HashSet). Map = key → value (HashMap). Pick by need, not by what you revised last.

For Iterator: ArrayList is the daily List: get(i) is fast, add at end is fast. HashMap lookup by key is average O(1). HashSet is unique values, no duplicates.

Use Iterator with generics: List<String>, Map<String, Integer>. Iterate with for-each or iterator. Don’t use a raw array when the size must grow.

Let's take this on the board with one tiny Main class — no extra files. Output: Asha scored 72 then Pass. Real Main. Swap marks/name to show one idea from Java Iterator. Start from main, go line by line, and stop at each print. That output is the proof for Iterator.

Exam tip

Explain Java Iterator as: definition → why → one code idea.

Example

// Java
public class Main {
  public static void main(String[] args) {
    int marks = 72;
    String name = "Asha";
    System.out.println(name + " scored " + marks);
    if (marks >= 40) System.out.println("Pass");
  }
}

Output: Asha scored 72 then Pass. Real Main. Swap marks/name to show one idea from Java Iterator.

Short notes

DefIterator — List = order + duplicates OK. Set = unique. Map = key → value.
RuleIterator — pick it only when that structure matches the problem.
RememberIterator — generics List<String>. ArrayList for daily lists. HashMap for lookup.
TrapIterator — using arrays for everything that must grow, or mixing List/Set/Map.

// Java public class Main { public static void main(String[] args) { int marks = 72; String name = "Asha"; System.out.println(name + " scored " + marks); if (marks >= 40) System.out.println("Pass"); } }

Java Iterator

Example

Short notes

Questions

Java Iterator

Example

Short notes

Questions