JDK8对List的简化操作-Lambda表达式

一时失言乱红尘 2022-06-06 03:05 215阅读 0赞

import java.util.*;
    import java.util.stream.Collectors;
    
    public class Test {
    	public static void main(String[] args) {
    		List<Student> list = new ArrayList<>();
    		Student student1 = new Student();student1.setAge("12");student1.setSex(0);
    		Student student2 = new Student();student2.setAge("13");student2.setSex(2);
    		Student student3 = new Student();student3.setAge("11");student3.setSex(1);
    		Student student4 = new Student();student4.setAge("18");student4.setSex(1);
    		Student student5 = new Student();student5.setAge("18");student5.setSex(0);
    		Student student6 = new Student();student6.setAge("18");student6.setSex(2);
    		Student student7 = new Student();student7.setAge("18");student7.setSex(2);
    		list.add(student1);
    		list.add(student2);
    		list.add(student3);
    		list.add(student4);
    		list.add(student5);
    		list.add(student6);
    		list.add(student7);
    		List<Demo> demos = new ArrayList<Demo>();
    		
    		// 原始数据
    		System.out.println("原始数据 组装list<demo>*******************");
    		demos = list.stream().map(student -> new Demo(student.getAge(), student.getSex())).collect(Collectors.toList());
    		demos.forEach(demo -> {
    			System.out.println("年龄 " + demo.getAge() + "  性别 " + demo.getSex() + ",");
    		});
    		
    		// 只取sex为0
    		System.out.println("只取sex为0****************");
    		List<Demo> demorm = demos.stream().filter(demo -> demo.getSex() == 0).distinct().collect(Collectors.toList());
    		demorm.forEach(demo -> {
    			System.out.println("年龄 " + demo.getAge() + "  性别 " + demo.getSex() + ",");
    		});
    		
    		// 筛选年龄大于12岁
    		System.out.println("筛选年龄大于12岁的*************");
    		List<Demo> demoFilter = demos.stream().filter(demo -> Integer.valueOf(demo.getAge()) > 12).collect(Collectors.toList());
    		demoFilter.forEach(demo -> {
    			System.out.println("年龄 " + demo.getAge() + "  性别 " + demo.getSex() + ",");
    		});
    		
    		// 排序
    		System.out.println("排序******************");
    		List<Demo> demoSort = demos.stream().sorted((s1, s2) -> s1.getAge().compareTo(s2.getAge())).collect(Collectors.toList());
    		demoSort.forEach(demo -> {
    			System.out.println("年龄 " + demo.getAge() + "  性别 " + demo.getSex() + ",");
    		});
    		
    		// 倒序
    		System.out.println("倒序****************");
    		ArrayList<Demo> demoArray = (ArrayList<Demo>) demos;
    		
    		Comparator<Demo> comparator = (h1, h2) -> h1.getAge().compareTo(h2.getAge());
    		demos.sort(comparator.reversed());
    		//or
    		demos.sort(Comparator.comparing(Demo::getAge).reversed());
    		
    		demos.forEach(demo -> {
    			System.out.println("年龄 " + demo.getAge() + "  性别 " + demo.getSex() + ",");
    		});
    		
    		// 多条件正序
    		System.out.println("多条件排序正序****************");
    		demoArray.sort(Comparator.comparing(Demo::getSex).thenComparing(Demo::getAge));
    		demoArray.forEach(demo -> {
    			System.out.println("年龄 " + demo.getAge() + "  性别 " + demo.getSex() + ",");
    		});
    		
    		// 多条件倒序
    		System.out.println("多条件排序倒序 sex  倒序****************");
    		demoArray.sort(Comparator.comparing(Demo::getSex).reversed().thenComparing(Demo::getAge));
    		demoArray.forEach(demo -> {
    			System.out.println("年龄 " + demo.getAge() + "  性别 " + demo.getSex() + ",");
    		});
    		
    		// 按照年龄分组
    		System.out.println("根据age分组结果为Map****************");
    		Map<String, List<Demo>> demoOder = demos.stream().collect(Collectors.groupingBy(Demo::getAge));
    		System.out.println(demoOder);
    	}
    }
    
    class Demo {
    	private String name;
    	private Integer sex;
    	private String age;
    
    	public Demo(String age, Integer sex) {
    		this.age = age;
    		this.sex = sex;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	public Integer getSex() {
    		return sex;
    	}
    
    	public void setSex(Integer sex) {
    		this.sex = sex;
    	}
    
    	public String getAge() {
    		return age;
    	}
    
    	public void setAge(String age) {
    		this.age = age;
    	}
    
    }
    
    class Student {
    	private String age;
    	private Integer sex;
    
    	public String getAge() {
    		return age;
    	}
    
    	public void setAge(String age) {
    		this.age = age;
    	}
    
    	public Integer getSex() {
    		return sex;
    	}
    
    	public void setSex(Integer sex) {
    		this.sex = sex;
    	}
    
    }