使用stream() 和map() 轉(zhuǎn)換元素：通過stream() 將集合轉(zhuǎn)為流，使用map() 應(yīng)用函數(shù)轉(zhuǎn)換每個(gè)元素，再通過collect() 收集結(jié)果；2. 將對(duì)象映射為不同類型：可提取對(duì)象字段或轉(zhuǎn)換類型，如用Person::getName 提取姓名；3. 鍊式操作：可連續(xù)調(diào)用map()、filter() 等方法實(shí)現(xiàn)多步處理；4. 使用不同收集器：可通過Collectors.toSet()、Collectors.joining() 等將結(jié)果收集為集合、字符串等形式；map() 是中間操作，需以collect() 等終止操作結(jié)束，原集合不變，推薦使用方法引用提升代碼可讀性。

Mapping a collection with streams in Java is a common and powerful operation that allows you to transform each element of a collection into another form using the Stream API introduced in Java 8.

The key method used for this is map() , which takes a Function as an argument and applies it to each element of the stream, producing a new stream with the transformed elements.

Here's how to do it step by step:

1. Use stream() and map() to transform elements

Start with a collection (like a List ), convert it to a stream, apply the map() operation, and collect the results back into a new collection.

 import java.util.*;
import java.util.stream.Collectors;

List<String> names = Arrays.asList("alice", "bob", "charlie");

List<String> upperCaseNames = names.stream()
    .map(String::toUpperCase)
    .collect(Collectors.toList());

System.out.println(upperCaseNames); // Output: [ALICE, BOB, CHARLIE]

In this example:

• stream() creates a stream from the list.
• map(String::toUpperCase) converts each string to uppercase.
• collect(Collectors.toList()) gathers the results into a new list.

2. Transform objects to different types

You can also map objects to entirely different types or extract specific fields.

For example, given a list of Person objects:

 class Person {
    String name;
    int age;

    Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    // getters...
    public String getName() { return name; }
    public int getAge() { return age; }
}

Extract just the names:

 List<Person> people = Arrays.asList(
    new Person("Alice", 25),
    new Person("Bob", 30)
);

List<String> names = people.stream()
    .map(Person::getName)
    .collect(Collectors.toList());

System.out.println(names); // Output: [Alice, Bob]

3. Chain multiple operations

Streams allow chaining multiple transformations and filters.

 List<Integer> lengths = people.stream()
    .map(Person::getName) // Get name (String)
    .map(String::length) // Get length of name
    .collect(Collectors.toList());

System.out.println(lengths); // Output: [5, 3]

Or with filtering:

 List<String> longNames = people.stream()
    .map(Person::getName)
    .filter(name -> name.length() > 3)
    .collect(Collectors.toList());

System.out.println(longNames); // Output: [Alice]

4. Use Collectors for different output types

You're not limited to List . You can collect into sets, maps, or even strings.

 Set<String> nameSet = people.stream()
    .map(Person::getName)
    .collect(Collectors.toSet());

String joinedNames = people.stream()
    .map(Person::getName)
    .collect(Collectors.joining(", "));

Key Points:

• map() is intermediate — it returns a new stream.
• Always end with a terminal operation like collect() , forEach() , or count() .
• The original collection remains unchanged — streams are non-destructive.
• Use method references ( Class::method ) when possible for cleaner code.

Basically, mapping a collection with streams is about transforming data cleanly and functionally. It's concise, readable, and widely used in modern Java code.

以上是如何用Java中的流繪製藏品？的詳細(xì)內(nèi)容。更多資訊請(qǐng)關(guān)注PHP中文網(wǎng)其他相關(guān)文章！