Beginner 20 min read

Parameters and Arguments

By the end of this lesson, you'll be able to:

  • Distinguish between a parameter (the placeholder) and an argument (the actual value passed in)
  • Write a method that accepts multiple parameters
  • Call the same method with different arguments

Prerequisites: "Writing Your First Method"

Parameter vs argument

public void logOrder(String customerName, Decimal orderTotal) {
    System.debug(customerName + ' ordered R' + orderTotal);
}

logOrder('Thabo', 450);
logOrder('Aisha', 1200);
  1. public void logOrder(String customerName, Decimal orderTotal) { — customerName and orderTotal are parameters — placeholders defined in the method signature.
  2. System.debug(customerName + ' ordered R' + orderTotal); — uses whatever values were passed in.
  3. } — closes the method.
  4. (blank line)
  5. logOrder('Thabo', 450); — 'Thabo' and 450 are arguments — the actual values supplied on this call.
  6. logOrder('Aisha', 1200); — same method, different arguments, different behavior each time.

A real business example: Agriculture (Crop Yield Logging)

public void logHarvest(String fieldName, Decimal tonnes, String cropType) {
    System.debug(fieldName + ' produced ' + tonnes + ' tonnes of ' + cropType);
}

logHarvest('North Field', 12.5, 'Maize');
logHarvest('South Field', 8.2, 'Wheat');
  1. public void logHarvest(String fieldName, Decimal tonnes, String cropType) { — three parameters this time.
  2. System.debug(fieldName + ' produced ' + tonnes + ' tonnes of ' + cropType); — builds one log message from all three.
  3. } — closes the method.
  4. (blank line)
  5. logHarvest('North Field', 12.5, 'Maize'); — one field's harvest.
  6. logHarvest('South Field', 8.2, 'Wheat'); — a different field, different crop, same method.

One method definition, reused across every field and crop — exactly the point of parameters: write the logging behavior once, apply it to any combination of inputs.

Order matters

Arguments are matched to parameters by position, not by name. logOrder(450, 'Thabo') would compile-error here since 450 isn't a String — but if the parameter types happened to line up, swapping the order would silently pass the wrong value to the wrong parameter. Always match the order defined in the method signature.

Exercise

Write a void method describeProduct that takes a String name and a Decimal price, and debugs them combined into one sentence. Call it with any product.

Show hint

public void describeProduct(String name, Decimal price) { ... }

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Execution Results

Run your code to see the result.

Parameters and Arguments Quiz

1. How are arguments matched to parameters when a method is called?

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Leaderboard

  • 1. Monde Masiza 1/1

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Summary

Parameters let a method work on different data each time it's called — the same method logic, applied to whatever values you actually pass in.

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