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Chapter 7: Problem 31

What is the difference between an ArrayList object's size and its capacity?

Short Answer

Expert verified
Answer: The size of an ArrayList represents the actual number of elements stored in it, while the capacity refers to the current space allocated for the ArrayList. Size changes when elements are added or removed, whereas capacity indicates the number of elements it can hold without needing to allocate additional memory. Understanding the properties of size and capacity is important for efficient memory management and improving the performance of a program.

Step by step solution

01

Understand ArrayList properties

An ArrayList in Java is a data structure that grows and shrinks dynamically, providing the ability to store objects without the need to specify its size upfront. It is important to understand two key properties of an ArrayList: size and capacity.
02

Define Size

The size of an ArrayList represents the actual number of elements stored in it. This changes when we add or remove elements from the ArrayList. For example, consider an empty ArrayList: ```java ArrayList names = new ArrayList<>(); ``` In this case, the size of the ArrayList `names` is 0.
03

Define Capacity

The capacity of an ArrayList represents the number of elements it can currently hold without needing to allocate additional memory. Initially, it has a default value (usually 10), but when the ArrayList reaches its capacity, it automatically grows to accommodate more elements. Returning to our example: ```java ArrayList names = new ArrayList<>(); ``` In this case, the initial capacity of the ArrayList `names` is 10 (assuming the default value).
04

Difference between Size and Capacity

The core difference between size and capacity lies in their purpose and behavior. The size of an ArrayList is the actual count of its elements, while capacity refers to the current space allocated for the ArrayList. For example: ```java ArrayList names = new ArrayList<>(); names.add("Alice"); names.add("Bob"); names.add("Charlie"); ``` Here, the size of the ArrayList is 3 (since it has three elements), while its capacity remains 10 (as no need to reallocate memory yet).
05

Importance of Size and Capacity

Understanding the difference between size and capacity is important because: 1. It helps in efficient memory management and avoiding unnecessary reallocation, which can improve the program's performance. 2. It allows developers to control the growth and shrinkage of the ArrayList by using methods like `ensureCapacity()` or `trimToSize()`, especially when dealing with large datasets or memory constraints.

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Most popular questions from this chapter

Recall that we discussed a Rectangle class in Chapter \(6 .\) Write code that declares a Rectangle array with five elements. Instantiate each element with a Rectangle object. Use the Rectangle constructor to initialize cach object with values for the Length and width ficlds.

a) Write a statement that declares a string array initialized with the following strings: "Mercury", "Venus", "Earth", and "Mars". b) Write a loop that displays the contents of cach element in the array you declared in A. c) Write a loop that displays the first character of the strings stored in cach element of the array you declared in A. (Hint: Use the string class's charat method discussed in Chaprer \(2 .\)

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