java——List的过滤排序分组

Posted 2022-12-19 如月之恒-

文章目录

• 方法实现
• 后言

方法实现

代码复制运行即可实现

public class Book implements Comparable<Book>
	private Integer id;
	private String name;
	private String type;
	
	
	public Book(Integer id, String name, String type) 
		super();
		this.id = id;
		this.name = name;
		this.type = type;
	


	public Integer getId() 
		return id;
	


	public void setId(Integer id) 
		this.id = id;
	


	public String getName() 
		return name;
	


	public void setName(String name) 
		this.name = name;
	


	public String getType() 
		return type;
	


	public void setType(String type) 
		this.type = type;
	


	@Override
	public String toString() 
		return "Book [id=" + id + ", name=" + name + ", type=" + type + "]";
	


	@Override
	public int compareTo(Book book) 
		return this.id-book.id;
	
	

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

public class ListTest 

	public static List<Book> prepareData() 
		List<Book> bookList = new ArrayList<>();
		for (int i = 0; i < 3; i++) 
			bookList.add(new Book(i, "book" + i, "心理学"));
		
		for (int i = 3; i < 6; i++) 
			bookList.add(new Book(i, "book" + i, "管理学"));
		
		for (int i = 6; i < 9; i++) 
			bookList.add(new Book(i, "book" + i, "编程"));
		
		return bookList;
	

	public static void main(String[] args) 
		List<Book> bookList = prepareData();

		/** 寻找的书籍Id **/
		ArrayList<Integer> ids = new ArrayList<>();
		ids.add(8);
		ids.add(5);
		ids.add(2);
		ids.add(6);
		List<Book> result = null;

		/** List过滤 **/
		System.out.println("************List过滤");
		result = bookList.stream().filter((Book b) -> ids.contains(b.getId())).collect(Collectors.toList());

		Collections.shuffle(result);/** 打乱List排序 **/
		if (result != null && !result.isEmpty()) 
			result.forEach(
					(Book b) -> System.out.println(String.format("%s-%s-%s", b.getId(), b.getName(), b.getType())));
		
		/**读取集合中的某个属性**/
		List<Integer> a = bookList.stream().map(Book::getId).collect(Collectors.toList());
		if (a != null && !a.isEmpty()) 
		    System.out.println("collect="+a.toString());
        

		
		/** List 排序 **/
		System.out.println("************List排序");
		
		Collections.sort(result);
		if (result != null && !result.isEmpty()) 
			result.forEach(
					(Book b) -> System.out.println(String.format("%s-%s-%s", b.getId(), b.getName(), b.getType())));
		
		
		/** List 统计 **/
		System.out.println("************List统计");
		long count = bookList.stream().filter(x -> x.getId()>5).count();
		System.out.println("id大于5的元素统计："+String.valueOf(count));

		/** list分组 **/
		System.out.println("************List分组");
		Map<String, List<Book>> groupBy = bookList.stream().collect(Collectors.groupingBy(Book::getType));
		System.out.println("groupBy:" + groupBy);
	

后言

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