Java · Theory

Java Deque Interface

Theory

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Java Deque Interface

Deque Interface 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 Deque Interface: 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 Deque Interface 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 Deque Interface. Start from main, go line by line, and stop at each print. That output is the proof for Deque Interface.

Exam tip

Explain Java Deque Interface 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 Deque Interface.

Short notes

DefDeque Interface — List = order + duplicates OK. Set = unique. Map = key → value.
RuleDeque Interface — pick it only when that structure matches the problem.
RememberDeque Interface — generics List<String>. ArrayList for daily lists. HashMap for lookup.
TrapDeque Interface — 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 Deque Interface

Example

Short notes

Questions

Java Deque Interface

Example

Short notes

Questions