JAVA | 58 - 類集框架 | Stream |

Stream：數據的加工處理操作。
MapReduce：Map：處理數據，Reduce：分析數據。

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;
import java.util.stream.Stream;

class Book{
    private String title;
    private int price;
    public Book(String title, int price){
        this.title = title;
        this.price = price;
    }
    @Override
    public String toString() {
        return this.title + " " + this.price;
    }
    @Override
    public boolean equals(Object obj) {
        if(obj == this){
            return true;
        }
        if(obj == null){
            return false;
        }
        if(!(obj instanceof Book)){
            return false;
        }
        Book book = (Book) obj;
        if(book.title.equals(this.title) && book.price == this.price){
            return true;
        }
        return false;
    }
}
public class Main {
    public static void main(String[] args) throws Exception{
        // 設置了泛型，從而保證集合中所有的數據類型都一致
        List <Book> list = new ArrayList <Book> ();
        Book bookA = new Book("java",100);
        Book bookB = new Book("c",89);
        Book bookC = new Book("c++",100);
        Book bookD = new Book("python",100);
        Collections.addAll(list,bookA,bookB,bookC,bookD,bookA,bookB,bookC,bookD);

        Stream <Book> stream = list.stream();
        // 去掉重複數據
        List <Book> list1 = stream.distinct().collect(Collectors.toList());
        System.out.println(list1);
        // 過濾數據
        Predicate <Book> predicate = (x) -> x.equals(bookA);
        List <Book> list2 = stream.filter(predicate).collect(Collectors.toList());
        System.out.println(list2);
    }
}