Hvordan sorterer man en ArrayList?

Jeg har en liste af doubler i java, og jeg ønsker at sortere ArrayList i faldende rækkefølge.

Input ArrayList er som nedenfor:

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);

Out put bør være som dette

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
Mahozad
Redigeret spørgsmål 2018ør juli 2018 в 7:23
Programmering
sorting java collections arraylist
2013ør april 2013 в 12:48
28 visninger
Løsning
Collections.sort(testList);
Collections.reverse(testList);

Det vil gøre, hvad du ønsker. Husk dog at importere Collections!

[Her er dokumentationen for Collections] (https://docs.oracle.com/javase/10/docs/api/java/util/Collections.html#sort(java.util.List)).

Carl Walsh
Redigeret svar 2018ør november 2018 в 11:59
Kommentarer (10)

Brug util-metoden i java.util.Collections klassen, dvs.

Collections.sort(list)

Hvis du vil sortere et brugerdefineret objekt, kan du faktisk bruge

Collections.sort(List list, Comparator<? super T> c)

se collections api

Elazar
Redigeret svar 2015ør august 2015 в 10:28
Kommentarer (0)
 
//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 synchronizedList = Collections.synchronizedList(new ArrayList());
        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 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;

    }
}
Hits sapra
Redigeret svar 2019ør januar 2019 в 10:57
Kommentarer (1)