Java之List集合排序

最新推荐文章于 2024-03-04 21:48:59 发布

原创最新推荐文章于 2024-03-04 21:48:59 发布 · 195 阅读

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本文通过示例介绍如何在Java中实现自定义对象的排序。首先展示了一个Book类，该类实现了Comparable接口并重写了compareTo方法以按单价升序排序。接着介绍了如何使用Comparator接口来对Double类型的列表进行升序排序。

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1.类实现Comparable<>接口

public class Book implements Comparable<Book>{
	
	private String bookname;
	
	private Double unitPrice;

	public String getBookname() {
		return bookname;
	}

	public void setBookname(String bookname) {
		this.bookname = bookname;
	}

	public Double getUnitPrice() {
		return unitPrice;
	}

	public void setUnitPrice(Double unitPrice) {
		this.unitPrice = unitPrice;
	}

	public Book(String bookname, Double unitPrice) {
		this.bookname = bookname;
		this.unitPrice = unitPrice;
	}

	public Book() {
		super();
	}
        //重写compareTo方法，按照unitPrice升序排序，降序的话将两个返回值互换即可
	@Override
	public int compareTo(Book book) {
		if(book.getUnitPrice()-this.unitPrice>=0){
			return -1;
		}
		return 1;
	}
         //重写toString方法，输出Book属性
	@Override
	public String toString() {
		return "Book [bookname=" + bookname + ", unitPrice=" + unitPrice + "]";
	}

}

public class CollectionsDemo {

	@Test
	public void test(){
		List<Book> books =new ArrayList<Book>();
		books.add(new Book("JAVA",100.00));
		books.add(new Book("JAVA",50.00));
		books.add(new Book("JAVA",70.00));
		books.add(new Book("JAVA",90.00));
		//未排序的集合
		printInfo(books);
		System.out.println("---------按照unitPrice排序后---------");
		//排序
                Collections.sort(books);
 		printInfo(books);
	}
	
	public void printInfo(List<Book> books){
		for(Book book:books){
			System.out.println(book);
		}
	}
}

2.Collections.sort(list,new Comparator<E>() {}
public int compare(Double o1, Double o2) {TODO//待实现}重写方法

public class CollectionsDemo {

	@Test
	public void test() {
		List<Double> listStr=new ArrayList<Double>();
		listStr.add(123.00);
		listStr.add(789.00);
		listStr.add(456.00);
		Collections.reverse(listStr);
		System.out.println("排序前");
		for(Double str:listStr) {
			System.out.println(str);
		}
		//按照unitPrice升序排序，降序的话将两个返回值互换即可
		Collections.sort(listStr,new Comparator<Double>() {
			@Override
			public int compare(Double o1, Double o2) {
				// TODO Auto-generated method stub
				return o1>o2?1:-1;
			}
		});
		System.out.println("排序后");
		for(Double str:listStr) {
			System.out.println(str);
		}
	}
}