国产av日韩一区二区三区精品,成人性爱视频在线观看,国产,欧美,日韩,一区,www.成色av久久成人,2222eeee成人天堂

Home Java javaTutorial Convert ArrayList to HashMap in Java

Convert ArrayList to HashMap in Java

Feb 07, 2025 am 11:23 AM
java

Convert ArrayList to HashMap in Java

The

interface in Java is a subinterface of the List interface, representing an ordered set, allowing duplicate elements. Collection is a commonly used implementation class for the ArrayList interface. It is a dynamic array without pre-specifying the size. List is a class in the Java collection framework, used to store key-value pairs. Keys cannot be repeated, and values ??can be repeated. HashMap<k v></k>

This article will introduce several methods to convert

to ArrayList: HashMap

    By iteration
  • ArrayList
  • Using Java 8 Stream API
The following are some examples:

<code>輸入列表:[1="1", 2="2", 3="3"]
輸出映射:{1=1, 2=2, 3=3}
輸入列表:[1="Java", 2="for", 3="JavaScript"]
輸出映射:{1=Java, 2=for, 3=JavaScript}
輸入:Mercedes, Audi, BMW, Harley Davidson, Triumph
輸出:{Car=[Mercedes, Audi, BMW], Bike=[Harley Davidson, Triumph]}</code>

Algorithm: Convert ArrayList to HashMap

This algorithm describes how to convert

to ArrayList. HashMap

  1. Step 1: Start.
  2. Step 2: Declare and import the necessary Java packages.
  3. Step 3: Create a public list.
  4. Step 4: Declare key-value pairs.
  5. Step 5: Create a constructor for the referenced value.
  6. Step 6: Assign values ??to the declared key.
  7. Step 7: Return the private variable id.
  8. Step 8: Declare a public class and method.
  9. Step 9: Declare the parameter string.
  10. Step 10: Create a . ArrayList
  11. Step 11: Use data elements to fill the list value.
  12. Step 12: Create and declare a mapping value.
  13. Step 13: Declare the object method.
  14. Step 14: Create an object map value.
  15. Step 15: Add each data element to the map.
  16. Step 16: Print the map value and end.

Syntax: Convert ArrayList to HashMap

The following are some sample code snippets:

ArrayList<product> productList = new ArrayList<product>();
productList = getProducts();
Map<string, product> urMap =
yourList.stream().collect(Collectors.toMap(Product::getField1,
Function.identity()));
HashMap<string, product> productMap = new HashMap<string, product>();
for (Product product : productList) {
   productMap.put(product.getProductCode(), product);
}
for (Product p: productList) { s.put(p.getName(), p); }
for(Product p : productList){
   s.put(p.getProductCode() , p);
}
These snippets show how to convert

to ArrayList. HashMap

Method

We will introduce two methods:

Method 1: Use iteration and Collectors.toMap() This method iterates directly

and adds each element to

. ArrayList HashMap

// 示例代碼 (假設(shè)ArrayList包含自定義對象)
class Color {
    private String name;
    private String code;
    // ... getters and setters ...
}

// ...

List<Color> colors = new ArrayList<>();
// ... populate colors list ...

Map<String, String> colorMap = colors.stream()
        .collect(Collectors.toMap(Color::getName, Color::getCode));
Method 2: Use Java 8 Stream API and

Collectors.groupingBy()If you need to group, you can use the method.

Collectors.groupingBy() Through the above methods, you can choose the appropriate method to convert

to
// 示例代碼 (假設(shè)ArrayList包含自定義對象,需要按類別分組)
class Product {
    private String category;
    private String name;
    // ... getters and setters ...
}

// ...

List<Product> products = new ArrayList<>();
// ... populate products list ...

Map<String, List<Product>> productMap = products.stream()
        .collect(Collectors.groupingBy(Product::getCategory));
according to actual needs. Remember to deal with potential duplicate keys, such as using the third parameter of

to specify the merge function. Select ArrayList to maintain the insertion order. HashMap

The above is the detailed content of Convert ArrayList to HashMap in Java. For more information, please follow other related articles on the PHP Chinese website!

Statement of this Website
The content of this article is voluntarily contributed by netizens, and the copyright belongs to the original author. This site does not assume corresponding legal responsibility. If you find any content suspected of plagiarism or infringement, please contact admin@php.cn

Hot AI Tools

Undress AI Tool

Undress AI Tool

Undress images for free

Undresser.AI Undress

Undresser.AI Undress

AI-powered app for creating realistic nude photos

AI Clothes Remover

AI Clothes Remover

Online AI tool for removing clothes from photos.

Clothoff.io

Clothoff.io

AI clothes remover

Video Face Swap

Video Face Swap

Swap faces in any video effortlessly with our completely free AI face swap tool!

Hot Tools

Notepad++7.3.1

Notepad++7.3.1

Easy-to-use and free code editor

SublimeText3 Chinese version

SublimeText3 Chinese version

Chinese version, very easy to use

Zend Studio 13.0.1

Zend Studio 13.0.1

Powerful PHP integrated development environment

Dreamweaver CS6

Dreamweaver CS6

Visual web development tools

SublimeText3 Mac version

SublimeText3 Mac version

God-level code editing software (SublimeText3)

Tips for Writing PHP Comments Tips for Writing PHP Comments Jul 18, 2025 am 04:51 AM

The key to writing PHP comments is to clarify the purpose and specifications. Comments should explain "why" rather than "what was done", avoiding redundancy or too simplicity. 1. Use a unified format, such as docblock (/*/) for class and method descriptions to improve readability and tool compatibility; 2. Emphasize the reasons behind the logic, such as why JS jumps need to be output manually; 3. Add an overview description before complex code, describe the process in steps, and help understand the overall idea; 4. Use TODO and FIXME rationally to mark to-do items and problems to facilitate subsequent tracking and collaboration. Good annotations can reduce communication costs and improve code maintenance efficiency.

Writing Effective PHP Comments Writing Effective PHP Comments Jul 18, 2025 am 04:44 AM

Comments cannot be careless because they want to explain the reasons for the existence of the code rather than the functions, such as compatibility with old interfaces or third-party restrictions, otherwise people who read the code can only rely on guessing. The areas that must be commented include complex conditional judgments, special error handling logic, and temporary bypass restrictions. A more practical way to write comments is to select single-line comments or block comments based on the scene. Use document block comments to explain parameters and return values at the beginning of functions, classes, and files, and keep comments updated. For complex logic, you can add a line to the previous one to summarize the overall intention. At the same time, do not use comments to seal code, but use version control tools.

Improving Readability with Comments Improving Readability with Comments Jul 18, 2025 am 04:46 AM

The key to writing good comments is to explain "why" rather than just "what was done" to improve the readability of the code. 1. Comments should explain logical reasons, such as considerations behind value selection or processing; 2. Use paragraph annotations for complex logic to summarize the overall idea of functions or algorithms; 3. Regularly maintain comments to ensure consistency with the code, avoid misleading, and delete outdated content if necessary; 4. Synchronously check comments when reviewing the code, and record public logic through documents to reduce the burden of code comments.

Effective PHP Commenting Effective PHP Commenting Jul 18, 2025 am 04:33 AM

The key to writing PHP comments is clear, useful and concise. 1. Comments should explain the intention behind the code rather than just describing the code itself, such as explaining the logical purpose of complex conditional judgments; 2. Add comments to key scenarios such as magic values, old code compatibility, API interfaces, etc. to improve readability; 3. Avoid duplicate code content, keep it concise and specific, and use standard formats such as PHPDoc; 4. Comments should be updated synchronously with the code to ensure accuracy. Good comments should be thought from the perspective of others, reduce the cost of understanding, and become a code understanding navigation device.

PHP Development Environment Setup PHP Development Environment Setup Jul 18, 2025 am 04:55 AM

The first step is to select the integrated environment package XAMPP or MAMP to build a local server; the second step is to select the appropriate PHP version according to the project needs and configure multiple version switching; the third step is to select VSCode or PhpStorm as the editor and debug with Xdebug; in addition, you need to install Composer, PHP_CodeSniffer, PHPUnit and other tools to assist in development.

Exploring Basic PHP Syntax Exploring Basic PHP Syntax Jul 17, 2025 am 04:11 AM

The basic PHP syntax includes: 1. Use wrapping code; 2. Use echo or print to output content, where echo supports multiple parameters; 3. Variables do not need to declare types, start with $. Common types include strings, integers, floating-point numbers, booleans, arrays and objects. Mastering these key points can help you get started with PHP development quickly.

Understanding PHP Variable Types Understanding PHP Variable Types Jul 17, 2025 am 04:12 AM

PHP has 8 variable types, commonly used include Integer, Float, String, Boolean, Array, Object, NULL and Resource. To view variable types, use the gettype() or is_type() series functions. PHP will automatically convert types, but it is recommended to use === to strictly compare the key logic. Manual conversion can be used for syntax such as (int), (string), etc., but be careful that information may be lost.

Understanding PHP Variables Understanding PHP Variables Jul 17, 2025 am 04:11 AM

PHP variables start with $, and the naming must follow rules, such as they cannot start with numbers and are case sensitive; the scope of the variable is divided into local, global and hyperglobal; global variables can be accessed using global, but it is recommended to pass them with parameters; mutable variables and reference assignments should be used with caution. Variables are the basis for storing data, and correctly mastering their rules and mechanisms is crucial to development.

See all articles