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Java TreeSet

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Java TreeSet

Set stores unique elements. HashSet — unordered, fast.

LinkedHashSet — insertion order.

TreeSet — sorted order.

Write one tiny example for TreeSet. Compile, print one result, and say the output out loud before you type.

Use TreeSet only when the problem needs it. Don’t force it into every program. Know one beginner trap.

Let's take this on the board with one tiny Main class — no extra files. Java TreeSet — duplicate A is ignored; size stays 2. Start from main, go line by line, and stop at each print. That output is the proof for TreeSet.

Exam tip

Pick Set type by: speed vs order vs sorted.

Example

import java.util.HashSet;
public class Main {
  public static void main(String[] args) {
    HashSet<String> set = new HashSet<>();
    set.add("A");
    set.add("B");
    set.add("A"); // ignored
    System.out.println(set.size()); // 2
    System.out.println(set.contains("B"));
  }
}

Java TreeSet — duplicate A is ignored; size stays 2.

Short notes

DefTreeSet is a Java idea you should explain with one small example.
RuleKnow the keyword / API used for TreeSet. Type a tiny Main and print one result.
RememberFor TreeSet, say the output before you code.
TrapTreeSet — only memorising the heading. No example, no trap.
Unique only
HashSet fast

import java.util.HashSet; public class Main { public static void main(String[] args) { HashSet<String> set = new HashSet<>(); set.add("A"); set.add("B"); set.add("A"); // ignored System.out.println(set.size()); // 2 System.out.println(set.contains("B")); } }

Java TreeSet

Example

Short notes

Questions

Java TreeSet

Example

Short notes

Questions