Java · Theory

Properties class

Theory

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Properties class

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

Exam tip

Explain Properties class as: definition → why → one code idea.

Example

// Properties
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 Properties class.

Short notes

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

// Properties 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"); } }

Properties class

Example

Short notes

Questions

Properties class

Example

Short notes

Questions