Question

Write a method sum that expects a List as a parameter. The method returns an int representing the sum of the integers in the list.

Short answer

Define sum method, initialize sum variable, loop through list adding each number to sum, return sum.

Step-by-step solution

Define the Method Signature

Begin by defining the method signature for the sum method. Since it is supposed to return an integer and takes a List of integers as a parameter, the signature should be: public int sum(List numbers)

Initialize a Sum Variable

Inside the sum method, declare and initialize a variable to store the sum of the integers in the list. For instance: int total = 0;

Iterate Over the List

Use a loop to iterate over each integer in the list. For example, you can use an enhanced for loop: for (Integer number : numbers)

Add Each Number to the Sum

Within the loop, add each integer to the sum variable. This can be achieved with: total += number;

Return the Sum

After the loop, return the sum variable. The complete method implementation should look like: public int sum(List numbers) { int total = 0; for (Integer number : numbers) { total += number; } return total;}

Key concepts

Method Signature

In Java, a method signature is an essential aspect to identify and declare a method. It includes the method name and parameters. For the `sum` method, we need it to return an integer and accept a `List` as input. The correct method signature is: `public int sum(List numbers)`.
Here’s a simplified explanation:

• `public`: This indicates that the method is accessible from anywhere.
• `int`: The return type of the method.
• `sum`: The name of the method.
• `List`: The parameter type and name, where `List` signifies a collection of `Integer` elements.

For Loop

A `for loop` is useful for iterating over a collection of items. In this exercise, we'll use an enhanced for loop to go through each integer in the `List`. The code looks like this: `for (Integer number : numbers)`.
This enhanced for loop does the following:

• `Integer number`: Declares a variable to hold each element in the list during iteration.
• `: numbers`: Indicates that we are looping through the collection named `numbers`.

By using this type of loop, we can access each integer in the list one by one.

List

A `List` is a collection that holds multiple `Integer` values. In Java, the `List` is part of the `java.util` package. This collection allows us to store and manage a sequence of integers efficiently.
When declaring a list, use the following syntax: `List numbers = new ArrayList<>();`.
Key points about `List`:

• It can dynamically grow or shrink in size.
• Supports various operations like adding, removing, and accessing elements.
• Provides an ordered sequence of elements.

Using a `List` makes handling a series of integers straightforward in Java.

Variable Initialization

Before using variables in a method, it's important to initialize them. In our `sum` method, we need a variable to store the sum of the list's integers. We initialize it with `int total = 0;`.
Here are some key points about variable initialization:

• Initialization provides an initial value to a variable.
• In this case, `total` starts at 0 to begin the sum calculation.
• It ensures that the variable has a defined value before its usage.

Proper initialization of variables is crucial to avoid errors during program execution.

Return Statement

The return statement ends the execution of a method and can return a value to the caller. In the `sum` method, after computing the sum of the integers, we return the `total` using `return total;`.
Understanding the return statement:

• It terminates the current method.
• Returns the specified value (`total` in this case) to the method’s caller.
• The return type of the value must match the method’s declared return type (`int` for our sum method).

This makes the method’s result usable outside of its scope.