In Java,ArrayandArrayListThey are all very common data structures, but they have their own advantages in usage scenarios, features and functions.
Understanding their differences is an important part of improving programming skills for junior Java engineers.
Below, I will compare these two in a simple and clear way.Data structure, and illustrate it through code examples.
Array (Array）
An array is a basic data structure that can store a fixed number of data items of the same type. The array must be created with a size specified, and once it is determined, its length cannot be changed. This means that arrays are suitable for storing known sizes and will not changeDatasetcombine.
Features:
- Fixed size: The length of the array is immutable after creation. If you need more space, you need to create a new array and transfer the data manually.
- Type safety: Arrays can store basic type data, such as int, double, etc., and directly save values, which is more efficient.
- Performance Advantages: Accessing array elements is very fast because it is directly located to the memory address through the index.
- Simple and direct: Arrays are simple to use and are the basic programming, but their functions are relatively single.
Code example:
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1int[] numbers = new int[5]; //Create a length of5integer array
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2numbers[0] = 1; //Direct assignment
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3(numbers[0]); //Access the first element
ArrayList
ArrayList is a dynamic array implementation in the Java collection framework. It inherits the List interface and can automatically resize.
ArrayList uses arrays internally to store elements, but unlike arrays, when elements exceed the current capacity, ArrayList will automatically increase the capacity to accommodate more elements.
Features:
- Dynamic size: ArrayList automatically manages capacity internally, and will automatically expand when the number of elements increases.
- Object storage: ArrayList can only store objects, and for basic types, they need to be wrapped classes such as Integer instead of int.
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Rich API: ArrayList provides many convenient methods such as
add(),remove(),size(),indexOf()etc., to facilitate operation of the collection. - flexibility: Due to variable capacity, ArrayList is ideal for handling data sets with uncertain amounts.
Code example:
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1import ;
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2
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3ArrayList<Integer> numbersList = new ArrayList<>(); //Create an ArrayList
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4numbersList.add(1); //Add elements
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5numbersList.add(2);
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6(numbersList.get(0)); //Access the first element
Comparison of arrays and ArrayList
- Memory allocation: The memory allocated when array is created is continuous. Although ArrayList uses arrays internally, it may lead to data migration during expansion, resulting in certain performance overhead.
- Type Limitations: Arrays can store basic types, while ArrayList stores object references, which require automatic boxing and unboxing, and there will be slight performance losses when operating on basic types.
- performance: For random access elements, arrays have better performance than ArrayList due to direct index addressing. However, ArrayList may perform better than arrays in insertion and deletion operations, especially in the middle position due to automatic scaling and data movement (arrays require manual moving elements).
- Use scenarios: If the data volume is fixed and not large, and the performance requirements are extremely high, you can choose an array. On the contrary, if the data volume changes dynamically or requires frequent addition and deletion operations, ArrayList will be a better choice.
Arrays and ArrayList each have their own advantages. Choosing which one to use requires a trade-off based on specific needs.
Arrays are simple and direct, suitable for fixed-size data storage; while ArrayList provides higher flexibility and convenient operation interfaces, suitable for processing dynamically-sized data collections.
Understanding their differences can help you make more appropriate choices when facing different scenarios.