創建自定義流

Question

我可以在Stream<String>中加載數據。 我正在使用流，因爲我無法加載內存中的所有數據，所以不允許收集。 我想要構建一個Stream<MyClass>來對MyClass的對象執行一些操作，爲流提供Stream<String>。

Answer 1

既然你已經有了一個Stream<String>和假設有像一個構造，只是寫：

Stream<MyClass> stream = stringStream.map(MyClass::new); 

Answer 2

Java示例：過濾收集不使用流

import java.util.ArrayList; 
import java.util.List; 


class Book{ 

    int book_id; 
    String book_name; 
    float price; 

    public Book() { 

    } 

    public Book(int book_id, String book_name, float price) { 
     this.book_id = book_id; 
     this.book_name = book_name; 
     this.price = price; 
    } 
} 

public class Mystringstream { 

    public static void main(String[] args) { 
    List<Book> booklist= new ArrayList<Book>(); 
    booklist.add(new Book(101,"java",500.25f)); 
    booklist.add(new Book(102,"php",300.20f)); 
    booklist.add(new Book(103,"c",400.34f)); 

    List<Float> bookpricelist=new ArrayList<Float>(); 
    for(Book book:booklist){ 
     if(book.price<500){ 
      bookpricelist.add(book.price); 

     } 
    } 
     System.out.println("Filter Book Price List: "+bookpricelist); 
    } 
} 

輸出：

過濾Book原價：300.2，400.34]

Java流實施例：過濾收集通過使用流

import java.util.ArrayList; 

import java.util.List; 

import java.util.stream.Collectors; 


class Book{ 
    int book_id; 
    String book_name; 
    float price; 

    public Book() { 

    } 

    public Book(int book_id, String book_name, float price) { 
     this.book_id = book_id; 
     this.book_name = book_name; 
     this.price = price; 
    } 
} 

public class Mystringstream { 

    public static void main(String[] args) { 

    List<Book> booklist= new ArrayList<Book>(); 
    booklist.add(new Book(101,"java",500.25f)); 
    booklist.add(new Book(102,"php",300.20f)); 
    booklist.add(new Book(103,"c",400.34f)); 

    List<Float> bookpricelist=booklist.stream().filter(p->p.price < 500).map(p->p.price).collect(Collectors.toList()); 

     System.out.println("Filter Book Price List: "+bookpricelist); 

    } 
} 

輸出： 過濾Book原價：300.2，400.34]