JAVA8 List最大值最小值求和平均值以及排序

Posted 2021-12-17 悟能的师兄

1：对象类型获取最大值、最小值、平均数

public static void main(String[] args) 
		List<User> uList=new ArrayList<User>();
		uList.add(new User(1, "xxx", 1, 18));
		uList.add(new User(2, "zzz", 1, 19));
		uList.add(new User(3, "aaa", 1, 20));
		uList.add(new User(4, "bbb", 1, 21));
		
		
		//最大年龄
		Integer maxAge=uList.stream().mapToInt(User::getAge).max().getAsInt();
		System.out.println("最大年龄为："+maxAge);
		//最小年龄
		Integer minAge=uList.stream().mapToInt(User::getAge).min().getAsInt();
		System.out.println("最小年龄为："+minAge);
		//年龄和
		Integer sumAge=uList.stream().mapToInt(User::getAge).sum();
		System.out.println("年龄和为："+sumAge);
		//年龄平均值
		double avgAge=uList.stream().mapToDouble(User::getAge).average().getAsDouble();
		System.out.println("年龄平均值为："+avgAge);
		
		double[] d=110.12,12.3,110.23,78.9;
		double minDouble=Arrays.stream(d).min().getAsDouble();
		System.out.println("最小数组值:"+minDouble);
		
		
	

2：number类型获取最大值、最小值、平均数

public static void main(String[] args) 
  List list  = new ArrayList();
   list.add(new Double(123.23));
   list.add(new Double(33.23));
   list.add(new Double(13.23));
   list.add(new Double(3.23));
   
   System.out.println(list);
   System.out.println("最大值: " + Collections.max(list));
   System.out.println("最小值: " + Collections.min(list));

   List<Integer> lists = list;
   DoubleSummaryStatistics statistics = lists.stream().mapToDouble(Number::doubleValue).summaryStatistics();
   
   System.out.println("最大值：" + statistics.getMax());
   System.out.println("最小值：" + statistics.getMin());
   System.out.println("平均值：" + statistics.getAverage());
   System.out.println("平均值四舍五入：" + Math.round(statistics.getAverage()));
   System.out.println("求和：" + statistics.getSum());
   System.out.println("计数：" + statistics.getCount());
   
 

3：对对象类型数据的list做排序

//测试数据，请不要纠结数据的严谨性
List<StudentInfo> studentList = new ArrayList<>();
studentList.add(new StudentInfo("李小明",true,18));
studentList.add(new StudentInfo("张小丽",false,21));
studentList.add(new StudentInfo("王大朋",true,19));
studentList.add(new StudentInfo("陈小跑",false,17));


//排序前输出
StudentInfo.printStudents(studentList);
//按年龄排序(Integer类型)   		使用年龄进行升序排序
List<StudentInfo> studentsSortName = studentList.stream().sorted(Comparator.comparing(StudentInfo::getAge)).collect(Collectors.toList());
//排序后输出
StudentInfo.printStudents(studentsSortName);



//排序前输出
StudentInfo.printStudents(studentList);
//按年龄排序(Integer类型)		使用年龄进行降序排序（使用reversed()方法）
List<StudentInfo> studentsSortName = studentList.stream().sorted(Comparator.comparing(StudentInfo::getAge).reversed()).collect(Collectors.toList());
//排序后输出
StudentInfo.printStudents(studentsSortName);



//排序前输出
StudentInfo.printStudents(studentList);
//按年龄排序(Integer类型)		使用年龄进行降序排序，年龄相同再使用身高升序排序
List<StudentInfo> studentsSortName = studentList.stream()
        .sorted(Comparator.comparing(StudentInfo::getAge).reversed().thenComparing(StudentInfo::getHeight))
        .collect(Collectors.toList());
//排序后输出
StudentInfo.printStudents(studentsSortName);