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Java ArrayList排序的3種方法

1. 使用Collections.sort()方法進(jìn)行排序

ArrayList 存儲(chǔ)著以字符串形式存在的國(guó)名(country name)，為了對(duì)這個(gè) ArrayList 進(jìn)行排序，你需要調(diào)用 Collections.sort()方法，傳遞由國(guó)名構(gòu)成的 ArrayList 對(duì)象。這種方法將按照自然順序(按字母升序)對(duì)元素(國(guó)名)進(jìn)行排序。代碼如下：

public class SortArrayListAscendingDescending {

private ArrayList arrayList;

public SortArrayListAscendingDescending(ArrayList arrayList) {

this.arrayList = arrayList;

}

public ArrayList getArrayList() {

return this.arrayList;

}

public ArrayList sortAscending() {

Collections.sort(this.arrayList);

return this.arrayList;

}

public ArrayList sortDescending() {

Collections.sort(this.arrayList, Collections.reverseOrder());

return this.arrayList;

}

}

在SortArrayListAscendingDescending類中，我們?cè)跇?gòu)造器中初始化了一個(gè) ArrayList 對(duì)象。在 sortAscending()方法中，我們調(diào)用了 Collections.sort()方法，并傳遞這個(gè)初始化的 ArrayList對(duì)象為參數(shù)，返回排序后的 ArrayList。在 sortDescending()方法中，我們調(diào)用重載的 Collections.sort()方法讓其按照降序?qū)υ嘏判?#xff0c;這個(gè)版本的 Collections.sort()接收ArrayList對(duì)象作為第一個(gè)參數(shù)，一個(gè)由 Collections.reverseOrder()方法返回的 Comparator 對(duì)象作為第二個(gè)參數(shù)。

public class SortArrayListAscendingDescendingTest {

public void testSortAscendingDescending() throws Exception {

ArrayList countryList = new ArrayList();

countryList.add("France");

countryList.add("USA");

countryList.add("India");

countryList.add("Spain");

countryList.add("England");

SortArrayListAscendingDescending sortArrayList = new SortArrayListAscendingDescending(countryList);

ArrayList unsortedArrayList = sortArrayList.getArrayList();

System.out.println("Unsorted ArrayList: " + unsortedArrayList);

ArrayList sortedArrayListAscending = sortArrayList.sortAscending();

System.out.println("Sorted ArrayList in Ascending Order : " +

sortedArrayListAscending);

ArrayList sortedArrayListDescending = sortArrayList.sortDescending();

System.out.println("Sorted ArrayList in Descending Order: " +

sortedArrayListDescending);

}

}

在SortArrayListAscendingDescendingTest測(cè)試代碼中，我們創(chuàng)建一個(gè) ArrayList 對(duì)象，并添加了 5 個(gè)字符串對(duì)象代表 5 個(gè)國(guó)家的名字。然后我們調(diào)用 getArrayList()、sortAscending()和 sortDescending()方法，并打印這些方法返回的 ArrayList 對(duì)象。

顯示結(jié)果：

-------------------------------------------------------

T E S T S

-------------------------------------------------------

Running guru.springframework.blog.sortarraylist.ascendingdescending.SortArrayListAscendingDescendingTest

Unsorted ArrayList: [France, USA, India, Spain, England]

Sorted ArrayList in Ascending Order : [England, France, India, Spain, USA]

Sorted ArrayList in Descending Order: [USA, Spain, India, France, England]

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.001 sec - in guru.springframework.blog.sortarraylis

2. 使用Comparable排序

讓我們來(lái)舉一個(gè)例子，JobCandidate 類的對(duì)象保存在 ArrayList 中并準(zhǔn)備對(duì)其進(jìn)行排序。JobCandidate 類有三個(gè)成員變量：字符串類型的姓名和性別、整型的年齡。我們想要對(duì)保存在 ArrayList 中的 JobCandidate 對(duì)象按照年齡進(jìn)行排序。因此我們要讓 JobCandidate 類實(shí)現(xiàn) Comparable 接口并重寫(xiě) compareTo()方法。

public class JobCandidate implements Comparable {

private String name;

private String gender;

private int age;

public JobCandidate(String name, String gender, int age) {

this.name = name;

this.gender = gender;

this.age = age;

}

public String getName() {

return name;

}

public String getGender() {

return gender;

}

public int getAge() {

return age;

}

@Override

public int compareTo(JobCandidate candidate) {

return ((this.getAge() < candidate.getAge()) ? (-1)

: ((this.getAge() == candidate.getAge())

? 0 : 1));

}

@Override

public String toString() {

return " Name: " + this.name + ", Gender: " + this.gender + ", age:" +

this.age;

}

}

JobCandidate 類被重寫(xiě)的 compareTo()方法中，我們實(shí)現(xiàn)了基于年齡的比較邏輯。

public class JobCandidateSorter {

ArrayList jobCandidate = new ArrayList<>();

public JobCandidateSorter(ArrayList jobCandidate) {

this.jobCandidate = jobCandidate;

}

public ArrayList getSortedJobCandidateByAge() {

Collections.sort(jobCandidate);

return jobCandidate;

}

}

在 JobCandidateSorter 類中，我們初始化了一個(gè) ArrayList 對(duì)象，委托方將通過(guò)構(gòu)造函數(shù)實(shí)例化 JobCandidateSorter 。然后我們編寫(xiě)了 getSortedJobCandidateByAge()方法，在這個(gè)方法中，我們調(diào)用 Collections.sort()并傳遞已經(jīng)初始化了的 ArrayList 為參數(shù)，最后返回排序后的 ArrayList。

public class JobCandidateSorterTest {

public void testGetSortedJobCandidateByAge() throws Exception {

JobCandidate jobCandidate1 = new JobCandidate("Mark Smith", "Male", 26);

JobCandidate jobCandidate2 = new JobCandidate("Sandy Hunt", "Female", 23);

JobCandidate jobCandidate3 = new JobCandidate("Betty Clark", "Female",

20);

JobCandidate jobCandidate4 = new JobCandidate("Andrew Styne", "Male", 24);

ArrayList jobCandidateList = new ArrayList();

jobCandidateList.add(jobCandidate1);

jobCandidateList.add(jobCandidate2);

jobCandidateList.add(jobCandidate3);

jobCandidateList.add(jobCandidate4);

JobCandidateSorter jobCandidateSorter = new JobCandidateSorter(jobCandidateList);

ArrayList sortedJobCandidate = jobCandidateSorter.getSortedJobCandidateByAge();

System.out.println("-----Sorted JobCandidate by age: Ascending-----");

for (JobCandidate jobCandidate : sortedJobCandidate) {

System.out.println(jobCandidate);

}

}

}

JobCandidateSorterTest類中，我們創(chuàng)建了四個(gè) JobCandidate 對(duì)象并把它們添加到 ArrayList，然后傳遞這個(gè) ArrayList 到構(gòu)造函數(shù)來(lái)實(shí)例化 JobCandidateSorter 類。最后，我們調(diào)用 JobCandidateSorter 類的 getSortedJobCandidateByAge()方法，并打印這個(gè)方法返回的排序后的 ArrayList。測(cè)試的輸出結(jié)果如下：

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T E S T S

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Running guru.springframework.blog.sortarraylist.comparable.JobCandidateSorterTest

-----Sorted JobCandidate by age: Ascending-----

Name: Betty Clark, Gender: Female, age:20

Name: Sandy Hunt, Gender: Female, age:23

Name: Andrew Styne, Gender: Male, age:24

Name: Mark Smith, Gender: Male, age:26

Tests run: 1, Failures: 0, Errors: 0, Skipped: 0, Time elapsed: 0.003 sec

- in guru.springframework.blog.sortarraylist.comparable.JobCandidateSorterTest

3.?使用 Comparator 排序

比如我有一個(gè)Person類,它的實(shí)例對(duì)象存儲(chǔ)在ArrayList數(shù)組中,現(xiàn)在要把ArrayList數(shù)組中的Person對(duì)象按照年齡排序.代碼如下：

Person類

public class Person {

String name;

int age;

public Person(String name, int age) {

this.name = name;

this.age = age;

}

public int getAge() {

return age;

}

public void setAge(int age) {

this.age = age;

}

public String getName() {

return name;

}

public void setName(String name) {

this.name = name;

}

}

Mycomparator類

public class Mycomparator implements Comparator {

public int compare(Object o1, Object o2) {

Person p1 = (Person) o1;

Person p2 = (Person) o2;

if (p1.age < p2.age) return 1;

else return 0;

}

}

ListSort類

public class ListSort {

public static void main(String[] args) {

ArrayList list = new ArrayList();

list.add(new Person("lcl", 28));

list.add(new Person("fx", 23));

list.add(new Person("wqx", 29));

Comparator comp = new Mycomparator();

Collections.sort(list, comp);

for (int i = 0; i < list.size(); i) {

Person p = (Person) list.get(i);

System.out.println(p.getName());

}

}

}

當(dāng)然，如果你的List包裝的是基本類型或者String，則只要 Collections.sort(list);即可

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