我在java中有一个双精度的列表，我想按降序排序数组列表。
输入数组列表如下:
List<Double> testList = new ArrayList();
testList.add(0.5);
testList.add(0.2);
testList.add(0.9);
testList.add(0.1);
testList.add(0.1);
testList.add(0.1);
testList.add(0.54);
testList.add(0.71);
testList.add(0.71);
testList.add(0.71);
testList.add(0.92);
testList.add(0.12);
testList.add(0.65);
testList.add(0.34);
testList.add(0.62);
输出应该是这样的
0.92
0.9
0.71
0.71
0.71
0.65
0.62
0.54
0.5
0.34
0.2
0.12
0.1
0.1
0.1
当前回答
在JAVA 8中，现在变得简单多了。
List<String> alphaNumbers = Arrays.asList("one", "two", "three", "four");
List<String> alphaNumbersUpperCase = alphaNumbers.stream()
.map(String::toUpperCase)
.sorted()
.collect(Collectors.toList());
System.out.println(alphaNumbersUpperCase); // [FOUR, ONE, THREE, TWO]
——反过来用这个
.sorted(Comparator.reverseOrder())
其他回答
//Here is sorted List alphabetically with syncronized
package com.mnas.technology.automation.utility;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.Iterator;
import java.util.List;
import org.apache.log4j.Logger;
/**
* @author manoj.kumar
*/
public class SynchronizedArrayList {
static Logger log = Logger.getLogger(SynchronizedArrayList.class.getName());
@SuppressWarnings("unchecked")
public static void main(String[] args) {
List<Employee> synchronizedList = Collections.synchronizedList(new ArrayList<Employee>());
synchronizedList.add(new Employee("Aditya"));
synchronizedList.add(new Employee("Siddharth"));
synchronizedList.add(new Employee("Manoj"));
Collections.sort(synchronizedList, new Comparator() {
public int compare(Object synchronizedListOne, Object synchronizedListTwo) {
//use instanceof to verify the references are indeed of the type in question
return ((Employee) synchronizedListOne).name
.compareTo(((Employee) synchronizedListTwo).name);
}
});
/*for( Employee sd : synchronizedList) {
log.info("Sorted Synchronized Array List..."+sd.name);
}*/
// when iterating over a synchronized list, we need to synchronize access to the synchronized list
synchronized (synchronizedList) {
Iterator<Employee> iterator = synchronizedList.iterator();
while (iterator.hasNext()) {
log.info("Sorted Synchronized Array List Items: " + iterator.next().name);
}
}
}
}
class Employee {
String name;
Employee(String name) {
this.name = name;
}
}
对于您的示例，这将在Java 8中发挥作用
List<Double> testList = new ArrayList();
testList.sort(Comparator.naturalOrder());
但是如果你想要排序对象的一些字段，你可以很容易地通过:
testList.sort(Comparator.comparing(ClassName::getFieldName));
or
testList.sort(Comparator.comparing(ClassName::getFieldName).reversed());
or
testList.stream().sorted(Comparator.comparing(ClassName::getFieldName).reversed()).collect(Collectors.toList());
来源:https://docs.oracle.com/javase/8/docs/api/java/util/Comparator.html
在JAVA 8中，现在变得简单多了。
List<String> alphaNumbers = Arrays.asList("one", "two", "three", "four");
List<String> alphaNumbersUpperCase = alphaNumbers.stream()
.map(String::toUpperCase)
.sorted()
.collect(Collectors.toList());
System.out.println(alphaNumbersUpperCase); // [FOUR, ONE, THREE, TWO]
——反过来用这个
.sorted(Comparator.reverseOrder())
使用java.util.Collections类的util方法，即
Collections.sort(list)
事实上，如果你想排序自定义对象你可以使用
Collections.sort(List<T> list, Comparator<? super T> c)
参见集合API
降:
Collections.sort(mArrayList, new Comparator<CustomData>() {
@Override
public int compare(CustomData lhs, CustomData rhs) {
// -1 - less than, 1 - greater than, 0 - equal, all inversed for descending
return lhs.customInt > rhs.customInt ? -1 : (lhs.customInt < rhs.customInt) ? 1 : 0;
}
});
