packagecom.concretepage;importjava.util.ArrayList;importjava.util.List;importjava.util.Map;importjava.util.function.Function;importjava.util.stream.Collectors;publicclassListToMap1 {publicstaticvoidmain(String[] args) { List<String> list =newArrayList<>(); list.add("Mohan"); list.add("Sohan"); ...
如果key重复,会报错 Exception in thread "main" java.lang.IllegalStateException: Duplicate key User{id=1, name='Tom', age=20} 1. 2. 如果key键重复,我们取后者 packagecom.github.mouday.reggie;importjava.util.Arrays;importjava.util.List;importjava.util.Map;importjava.util.function.Function;import...
package com.github.mouday.reggie;import java.util.Arrays;import java.util.List;import java.util.Map;import java.util.function.Function;import java.util.stream.Collectors;public class Demo {public static void main(String[] args) {List<User> users = Arrays.asList(new User(1, "Tom", 20),new...
当需要将一个List转换为Map时,可以使用 Java 8 中的Collectors.toMap()方法,Map是由key-value组成的键值对集合,在使用Collectors.toMap()方法时,如果值为空,会报空指针异常,下面通过一个实例来验证一下。 首先定义一个Student.java类 packagecom.magic.npe;publicclassStudent{privateString name;privateInteger age;...
("Employees in employeeLinkedList: " + employeeLinkedList); } } //Employee.java(POJO class) package com.javabrahman.java8.collector; public class Employee { private String name; private Integer age; private Double salary; public Employee(String name, Integer age, Double salary) { this.name =...
再创建一个Test.java类,用来验证将List<Staff>转换为Map<String, List<Staff>>,即按年龄将员工进行分组。 packagecom.magic.stream;importjava.util.ArrayList;importjava.util.List;importjava.util.Map;importjava.util.stream.Collectors;publicclassTest{publicstaticvoidmain(String[]args){List<Staff>staffs=newArr...
package com.javabrahman.java8; import java.text.DecimalFormat; public class Employee { private String name; private Integer age; private Double salary; public Employee(String name, Integer age, Double salary) { this.name = name; this.age = age; ...
当需要将一个List转换为Map时,可以使用 Java 8 中的 Collectors.toMap() 方法,Map是由key-value组成的键值对集合,在使用Collectors.toMap() 方法时,如果...
java8之stream 2019-12-02 18:26 −今天看到一篇关于java8的文章,发现有些特性在日常没用到,所以也完全不了解,然后学习了一波: (主要包含:Map, FlatMap, reduce, groupingBy, joining, reducing, parallelStream, peek 等) package cn.miaoyin...
Stream toList()返回的是只读List原则上不可修改,collect(Collectors.toList())默认返回的是ArrayList,可以增删改查