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Java Map Interface

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Java Map Interface

Map stores key → value pairs. Keys are unique.

HashMap common; TreeMap sorted keys; LinkedHashMap keeps order.

Iterate entrySet() for both key and value.

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

Use Map Interface 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 Map Interface — treeMap prints keys in sorted order. Start from main, go line by line, and stop at each print. That output is the proof for Map Interface.

Exam tip

Say which Map keeps sorted keys (TreeMap).

Example

import java.util.TreeMap;
public class Main {
  public static void main(String[] args) {
    TreeMap<String, Integer> m = new TreeMap<>();
    m.put("b", 2);
    m.put("a", 1);
    System.out.println(m); // {a=1, b=2}
  }
}

Java Map Interface — treeMap prints keys in sorted order.

Short notes

DefMap Interface is a Java idea you should explain with one small example.
RuleKnow the keyword / API used for Map Interface. Type a tiny Main and print one result.
RememberFor Map Interface, say the output before you code.
TrapMap Interface — only memorising the heading. No example, no trap.
key → value
Unique keys

import java.util.TreeMap; public class Main { public static void main(String[] args) { TreeMap<String, Integer> m = new TreeMap<>(); m.put("b", 2); m.put("a", 1); System.out.println(m); // {a=1, b=2} } }

Java Map Interface

Example

Short notes

Questions

Java Map Interface

Example

Short notes

Questions