Java8 List统计（最大值，最小值、平均值、总和）

深碍√TFBOYSˉ_ 2023-10-10 13:54 67阅读 0赞

### 核心功能代码： ###

Integer sum = list.stream().mapToInt(User::getAge).sum();
            System.out.println("年龄总和：" +sum);
            Integer max = list.stream().mapToInt(User::getAge).max().orElse(0);
            System.out.println("年龄 最大：" + max);
            Integer min = list.stream().mapToInt(User::getAge).min().orElse(0);
            System.out.println("年龄 最小：" + min);
            Double average = list.stream().mapToInt(User::getAge).average().orElse(0l);
            System.out.println("年龄 平均：" + df.format(average));

Java8 Stream除了支持Int类型，还支持double 类型和long类型

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT_size_8_color_FFFFFF_t_70_g_se_x_16][]

**学生年龄实例：**

package com.digipower.test;
    
    import java.text.DecimalFormat;
    import java.util.ArrayList;
    import java.util.List;
    import java.util.Random;
    
    public class ListTest {
    	private static final DecimalFormat df = new DecimalFormat("0.00");//保留两位小数点
    
    	public static void main(String[] args) {
    		Random random = new Random();
    		List<User> list = new ArrayList<User>();
    		for (int i = 1; i <= 5; i++) {
    			int age = random.nextInt(10) + 5;// 随机年龄：10-15
    			User u = new User(String.valueOf(i), "用户-" + i, age);
    			list.add(u);
    		}
    		Integer sum = list.stream().mapToInt(User::getAge).sum();
            System.out.println("年龄总和：" +sum);
            Integer max = list.stream().mapToInt(User::getAge).max().orElse(0);
            System.out.println("年龄 最大：" + max);
            Integer min = list.stream().mapToInt(User::getAge).min().orElse(0);
            System.out.println("年龄 最小：" + min);
            Double average = list.stream().mapToInt(User::getAge).average().orElse(0l);
            System.out.println("年龄 平均：" + df.format(average));
    	}
    
    	static class User {
    		private String id;
    		private String name;
    		private int age;
    
    		public String getId() {
    			return id;
    		}
    
    		public void setId(String id) {
    			this.id = id;
    		}
    
    		public String getName() {
    			return name;
    		}
    
    		public void setName(String name) {
    			this.name = name;
    		}
    
    		public int getAge() {
    			return age;
    		}
    
    		public void setAge(int age) {
    			this.age = age;
    		}
    
    		public User(String id, String name, int age) {
    			super();
    			this.id = id;
    			this.name = name;
    			this.age = age;
    		}
    
    	}
    
    }

**效果截图：**

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT_size_17_color_FFFFFF_t_70_g_se_x_16][]

**溫馨提示：針對金融数据类型BigDecimal，求和方式必须使用Stream 类中的reduce函数**

**学生余额实例：**

package com.digipower.test;
    
    import java.math.BigDecimal;
    import java.text.DecimalFormat;
    import java.util.ArrayList;
    import java.util.List;
    import java.util.Optional;
    import java.util.Random;
    
    public class ListTest {
    	private static final DecimalFormat df = new DecimalFormat("0.00");//保留两位小数点
    
    	public static void main(String[] args) {
    		Random random = new Random();
    		List<User> list = new ArrayList<User>();
    		for (int i = 1; i <= 5; i++) {
    			int age = random.nextInt(10) + 5;// 随机年龄：10-15
    			User u = new User(String.valueOf(i), "用户-" + i, age);
    			double balance = random.nextDouble() * 100 + 100;//随机金额：100-200
    			u.setBalance(new BigDecimal(balance).setScale(BigDecimal.ROUND_HALF_UP, 2));
    			list.add(u);
    		}
    		Integer sum = list.stream().mapToInt(User::getAge).sum();
            System.out.println("年龄总和：" +sum);
            Integer max = list.stream().mapToInt(User::getAge).max().orElse(0);
            System.out.println("年龄 最大：" + max);
            Integer min = list.stream().mapToInt(User::getAge).min().orElse(0);
            System.out.println("年龄 最小：" + min);
            Double average = list.stream().mapToInt(User::getAge).average().orElse(0l);
            System.out.println("年龄 平均：" + df.format(average));
            
            BigDecimal add = list.stream().map(User::getBalance).reduce(BigDecimal.ZERO, BigDecimal::add);
            System.out.println("金额 总和：" + df.format(add));
            Optional<User> maxBalance = list.stream().max((u1, u2) -> u1.getBalance().compareTo(u2.getBalance()));
            System.out.println("金额 最高：" + df.format(maxBalance.get().getBalance()));
            Optional<User> minBalance = list.stream().min((u1, u2) -> u1.getBalance().compareTo(u2.getBalance()));
            System.out.println("金额 最低：" + df.format(minBalance.get().getBalance()));
    	}
    
    	static class User {
    		private String id;
    		private String name;
    		private int age;
    		private BigDecimal balance;
    
    		public String getId() {
    			return id;
    		}
    
    		public void setId(String id) {
    			this.id = id;
    		}
    
    		public String getName() {
    			return name;
    		}
    
    		public void setName(String name) {
    			this.name = name;
    		}
    
    		public int getAge() {
    			return age;
    		}
    
    		public void setAge(int age) {
    			this.age = age;
    		}
    		
    		
    
    		public BigDecimal getBalance() {
    			return balance;
    		}
    
    		public void setBalance(BigDecimal balance) {
    			this.balance = balance;
    		}
    
    		public User(String id, String name, int age) {
    			super();
    			this.id = id;
    			this.name = name;
    			this.age = age;
    		}
    
    	}
    
    }

**效果截图**：

![watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT_size_20_color_FFFFFF_t_70_g_se_x_16][]

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[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT_size_17_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/c3289fbe17014e5a8243a2f22bfaabde.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT,size_17,color_FFFFFF,t_70,g_se,x_16
[watermark_type_d3F5LXplbmhlaQ_shadow_50_text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT_size_20_color_FFFFFF_t_70_g_se_x_16]: https://img-blog.csdnimg.cn/d2402be90bb6476794f544ddb0bd107f.png?x-oss-process=image/watermark,type_d3F5LXplbmhlaQ,shadow_50,text_Q1NETiBA5Zyo5aWL5paX55qE5aSn6YGT,size_20,color_FFFFFF,t_70,g_se,x_16