在Java中使用stream.sorted()对列表进行排序
我对从流中排序列表感兴趣。这是我正在使用的代码:在Java中使用stream.sorted()对列表进行排序,java,list,sorting,java-stream,Java,List,Sorting,Java Stream,我对从流中排序列表感兴趣。这是我正在使用的代码: list.stream() .sorted((o1, o2)->o1.getItem().getValue().compareTo(o2.getItem().getValue())) .collect(Collectors.toList()); 我错过什么了吗?列表未排序 它应该根据具有最低值的项目对列表进行排序 for (int i = 0; i < list.size(); i++) { System.ou
list.stream()
.sorted((o1, o2)->o1.getItem().getValue().compareTo(o2.getItem().getValue()))
.collect(Collectors.toList());
我错过什么了吗?列表未排序
它应该根据具有最低值的项目对列表进行排序
for (int i = 0; i < list.size(); i++)
{
System.out.println("list " + (i+1));
print(list, i);
}
for(int i=0;i
以及打印方法:
public static void print(List<List> list, int i)
{
System.out.println(list.get(i).getItem().getValue());
}
公共静态无效打印(列表,int i)
{
System.out.println(list.get(i.getItem().getValue());
}
它似乎工作正常:
List<BigDecimal> list = Arrays.asList(new BigDecimal("24.455"), new BigDecimal("23.455"), new BigDecimal("28.455"), new BigDecimal("20.455"));
System.out.println("Unsorted list: " + list);
final List<BigDecimal> sortedList = list.stream().sorted((o1, o2) -> o1.compareTo(o2)).collect(Collectors.toList());
System.out.println("Sorted list: " + sortedList);
您确定您不是在验证列表而不是
sortedList
[在上面的示例中],即您正在将stream()
的结果存储在一个新的list
对象中并验证该对象吗?这与Collections.sort()
中的参数引用被排序不同。在这种情况下,您只需获得一个排序流,最终需要收集并分配给另一个变量:
List result = list.stream().sorted((o1, o2)->o1.getItem().getValue().
compareTo(o2.getItem().getValue())).
collect(Collectors.toList());
您刚刚错过了分配结果请改用:
并通过以下方式使其更加简洁:
在这两者之后,列表
本身将被排序
你的问题是
返回已排序的数据,但它没有按预期进行排序。Collection itemCollection=basket.values();
Collection<Map<Item, Integer>> itemCollection = basket.values();
Iterator<Map<Item, Integer>> itemIterator = itemCollection.stream().sorted(new TestComparator()).collect(Collectors.toList()).iterator();
package com.ie.util;
import com.ie.item.Item;
import java.util.Comparator;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class TestComparator implements Comparator<Map<Item, Integer>> {
// comparator is used to sort the Items based on the price
@Override
public int compare(Map<Item, Integer> o1, Map<Item, Integer> o2) {
// System.out.println("*** compare method will be called *****");
Item item1 = null;
Item item2 = null;
Set<Item> itemSet1 = o1.keySet();
Iterator<Item> itemIterator1 = itemSet1.iterator();
if(itemIterator1.hasNext()){
item1 = itemIterator1.next();
}
Set<Item> itemSet2 = o2.keySet();
Iterator<Item> itemIterator2 = itemSet2.iterator();
if(itemIterator2.hasNext()){
item2 = itemIterator2.next();
}
return -item1.getPrice().compareTo(item2.getPrice());
}
}
迭代器Iterator=itemCollection.stream().sorted(新的TestComparator()).collect(Collectors.toList()).Iterator();
包com.ie.util;
导入com.ie.item.item;
导入java.util.Comparator;
导入java.util.Iterator;
导入java.util.Map;
导入java.util.Set;
公共类TestComparator实现了Comparator{
//比较器用于根据价格对项目进行排序
@凌驾
公共整数比较(映射o1,映射o2){
//System.out.println(“***比较方法将被调用******”);
item1=null;
item2=null;
Set itemSet1=o1.keySet();
迭代器iterator1=itemSet1.Iterator();
if(itemIterator1.hasNext()){
item1=itemIterator1.next();
}
Set itemSet2=o2.keySet();
迭代器iterator2=itemSet2.Iterator();
if(itemIterator2.hasNext()){
item2=itemIterator2.next();
}
return-item1.getPrice().compareTo(item2.getPrice());
}
}
****这有助于对嵌套的map对象进行排序,如map>,这里我根据项目对象价格进行了排序。Java8提供了不同的实用程序api方法,帮助我们更好地对流进行排序 如果您的列表是一个整数列表(或Double、Long、String等),那么您可以使用java提供的默认比较器对列表进行排序
List<Integer> integerList = Arrays.asList(1, 4, 3, 4, 5);
当没有参数传递给sorted()时,使用java 8提供的默认比较器:
integerList.stream().sorted((i1, i2) -> i1.compareTo(i2)).forEach(System.out::println);
integerList.stream().sorted().forEach(System.out::println); //Natural order
integerList.stream().sorted(Comparator.reverseOrder()).forEach(System.out::println); // Reverse Order
List<Person> personList = Arrays.asList(new Person(1000, "First", 25, 30000),
new Person(2000, "Second", 30, 45000),
new Person(3000, "Third", 35, 25000));
personList.stream().sorted((p1, p2) -> ((Long)p1.getPersonId()).compareTo(p2.getPersonId()))
.forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparingLong(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId).thenComparing(Person::getAge)).forEach(person -> System.out.println(person.getName())); //Sorting by person id and then by age.
如果要按相反顺序对同一列表排序:
integerList.stream().sorted((i1, i2) -> i1.compareTo(i2)).forEach(System.out::println);
integerList.stream().sorted().forEach(System.out::println); //Natural order
integerList.stream().sorted(Comparator.reverseOrder()).forEach(System.out::println); // Reverse Order
List<Person> personList = Arrays.asList(new Person(1000, "First", 25, 30000),
new Person(2000, "Second", 30, 45000),
new Person(3000, "Third", 35, 25000));
personList.stream().sorted((p1, p2) -> ((Long)p1.getPersonId()).compareTo(p2.getPersonId()))
.forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparingLong(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId).thenComparing(Person::getAge)).forEach(person -> System.out.println(person.getName())); //Sorting by person id and then by age.
如果您的列表是用户定义对象的列表,则:
integerList.stream().sorted((i1, i2) -> i1.compareTo(i2)).forEach(System.out::println);
integerList.stream().sorted().forEach(System.out::println); //Natural order
integerList.stream().sorted(Comparator.reverseOrder()).forEach(System.out::println); // Reverse Order
List<Person> personList = Arrays.asList(new Person(1000, "First", 25, 30000),
new Person(2000, "Second", 30, 45000),
new Person(3000, "Third", 35, 25000));
personList.stream().sorted((p1, p2) -> ((Long)p1.getPersonId()).compareTo(p2.getPersonId()))
.forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparingLong(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId).thenComparing(Person::getAge)).forEach(person -> System.out.println(person.getName())); //Sorting by person id and then by age.
使用Comparator.comparingLong()方法(我们还有comparingDouble()和comparingInt()方法):
integerList.stream().sorted((i1, i2) -> i1.compareTo(i2)).forEach(System.out::println);
integerList.stream().sorted().forEach(System.out::println); //Natural order
integerList.stream().sorted(Comparator.reverseOrder()).forEach(System.out::println); // Reverse Order
List<Person> personList = Arrays.asList(new Person(1000, "First", 25, 30000),
new Person(2000, "Second", 30, 45000),
new Person(3000, "Third", 35, 25000));
personList.stream().sorted((p1, p2) -> ((Long)p1.getPersonId()).compareTo(p2.getPersonId()))
.forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparingLong(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId).thenComparing(Person::getAge)).forEach(person -> System.out.println(person.getName())); //Sorting by person id and then by age.
使用Comparator.comparing()方法(基于提供的getter方法进行比较的通用方法):
integerList.stream().sorted((i1, i2) -> i1.compareTo(i2)).forEach(System.out::println);
integerList.stream().sorted().forEach(System.out::println); //Natural order
integerList.stream().sorted(Comparator.reverseOrder()).forEach(System.out::println); // Reverse Order
List<Person> personList = Arrays.asList(new Person(1000, "First", 25, 30000),
new Person(2000, "Second", 30, 45000),
new Person(3000, "Third", 35, 25000));
personList.stream().sorted((p1, p2) -> ((Long)p1.getPersonId()).compareTo(p2.getPersonId()))
.forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparingLong(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId).thenComparing(Person::getAge)).forEach(person -> System.out.println(person.getName())); //Sorting by person id and then by age.
我们也可以使用比较()方法进行链接:
integerList.stream().sorted((i1, i2) -> i1.compareTo(i2)).forEach(System.out::println);
integerList.stream().sorted().forEach(System.out::println); //Natural order
integerList.stream().sorted(Comparator.reverseOrder()).forEach(System.out::println); // Reverse Order
List<Person> personList = Arrays.asList(new Person(1000, "First", 25, 30000),
new Person(2000, "Second", 30, 45000),
new Person(3000, "Third", 35, 25000));
personList.stream().sorted((p1, p2) -> ((Long)p1.getPersonId()).compareTo(p2.getPersonId()))
.forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparingLong(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId)).forEach(person -> System.out.println(person.getName()));
personList.stream().sorted(Comparator.comparing(Person::getPersonId).thenComparing(Person::getAge)).forEach(person -> System.out.println(person.getName())); //Sorting by person id and then by age.
个人类别
public class Person {
private long personId;
private String name;
private int age;
private double salary;
public long getPersonId() {
return personId;
}
public void setPersonId(long personId) {
this.personId = personId;
}
public Person(long personId, String name, int age, double salary) {
this.personId = personId;
this.name = name;
this.age = age;
this.salary = salary;
}
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 double getSalary() {
return salary;
}
public void setSalary(double salary) {
this.salary = salary;
}
}
这是一个简单的例子:
List<String> citiesName = Arrays.asList( "Delhi","Mumbai","Chennai","Banglore","Kolkata");
System.out.println("Cities : "+citiesName);
List<String> sortedByName = citiesName.stream()
.sorted((s1,s2)->s2.compareTo(s1))
.collect(Collectors.toList());
System.out.println("Sorted by Name : "+ sortedByName);
List citiesName=Arrays.asList(“德里”、“孟买”、“钦奈”、“班格罗尔”、“加尔各答”);
System.out.println(“城市:+citiesName”);
List sortedByName=citiesName.stream()
.已排序((s1,s2)->s2.与(s1)比较)
.collect(Collectors.toList());
System.out.println(“按名称排序:+sortedByName”);
您的IDE可能没有获得JDK1.8或更高版本来编译代码
为您的_项目设置Java版本1.8>属性>项目方面>Java版本1.8
这可能有助于人们在这里搜索如何按字母顺序对列表排序。
导入lombok.Getter;
进口龙目织机;
进口龙目草;
导入java.util.ArrayList;
导入java.util.Comparator;
导入java.util.List;
公共类分拣服务{
公共静态void main(字符串[]args){
列表测试=新建ArrayList();
添加(准备测试数据(“Asmin”,1));
测试。添加(准备测试数据(“saurav”,4));
添加(准备测试数据(“asmin”,2));
测试。添加(准备测试数据(“Saurav”,3));
test.forEach(数据->系统输出.println(数据));
/**输出
*TestData(name=Asmin,id=1)
*TestData(name=saurav,id=4)
*TestData(name=asmin,id=2)
*TestData(name=Saurav,id=3)
*/
sort(Comparator.comparing(TestData::getName,String::compareToIgnoreCase));
test.forEach(数据->系统输出.println(数据));
/**排序输出
*TestData(name=Asmin,id=1)
*TestData(name=asmin,id=2)
*TestData(name=saurav,id=4)
*TestData(name=Saurav,id=3)
*/
}
私有静态测试数据prepareTestData(字符串名称,int-id){
TestData TestData=新的TestData();
testData.setId(id);
testData.setName(name);
返回测试数据;
}
}
@吸气剂
@塞特
@托斯特林
类测试数据{
私有字符串名称;
私有int-id;
}
使用streamAPI对整数排序
arr.stream()
.sorted((item1,item2)->Integer.compare(item1.price,item2.price))
.forEach(项目->项目.show());
//asc
System.out.println(“------------------”);
//描述
arr.stream()
.sorted((item1,item2)->item1.priceitem.show());
list.sort(Comparator.comparing(o->o.getItem().getValue())代码>对我来说是新的。伟大的我觉得这个答案对于这个问题来说太详细了,但根本没有解决这个问题。在自答的Q/A中使用这个答案。我也觉得这是最好和正确的答案。使用Comparator.comparating*
是更好、更面向JDK8的方法