Java · Theory

Java Varargs

Theory

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Java Varargs

Varargs is modern Java (5/8 toolkit). Lambdas are short functions: (n) -> print. They implement a functional interface (one abstract method). Streams let you filter/map/collect a list without a manual loop.

For Varargs: generics keep types safe: List<String>. Autoboxing turns int into Integer when needed. varargs is String... args. Optional avoids some null checks — don’t overuse it.

Keep Varargs small. Don’t dump business logic inside forEach. Know one tiny example you can write from memory.

Let's take this on the board with one tiny Main class — no extra files. Java Varargs — output: 10. sum(2, 3, 5) — varargs is a real int[] behind the scenes. 2+3+5=10. Start from main, go line by line, and stop at each print. That output is the proof for Varargs.

Exam tip

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

Example

public class Main {
  static int sum(int... n) {
    int s = 0;
    for (int x : n) s += x;
    return s;
  }
  public static void main(String[] args) {
    System.out.println(sum(2, 3, 5));
  }
}

Java Varargs — output: 10. sum(2, 3, 5) — varargs is a real int[] behind the scenes. 2+3+5=10.

Short notes

DefVarargs is part of modern Java (generics / Java 8 style).
RuleVarargs — lambda = (args) -> body on a functional interface.
UseVarargs — streams filter/map/collect. Generics = List<String>.
TrapVarargs — huge logic inside lambdas, or forgetting generics.

Java · Theory

Java Varargs

← All stacks

Theory

229/270

Java Varargs

For Varargs: generics keep types safe: List<String>. Autoboxing turns int into Integer when needed. varargs is String... args. Optional avoids some null checks — don’t overuse it.

Keep Varargs small. Don’t dump business logic inside forEach. Know one tiny example you can write from memory.

Exam tip

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

Example

public class Main {
  static int sum(int... n) {
    int s = 0;
    for (int x : n) s += x;
    return s;
  }
  public static void main(String[] args) {
    System.out.println(sum(2, 3, 5));
  }
}

Java Varargs — output: 10. sum(2, 3, 5) — varargs is a real int[] behind the scenes. 2+3+5=10.

Short notes

DefVarargs is part of modern Java (generics / Java 8 style).
RuleVarargs — lambda = (args) -> body on a functional interface.
UseVarargs — streams filter/map/collect. Generics = List<String>.
TrapVarargs — huge logic inside lambdas, or forgetting generics.

Java Varargs

Example

Short notes

Questions

Java Varargs

Example

Short notes

Questions