Java中的各種集合排序

更新時間：2021-05-06 11:39:30 來源：動力節點瀏覽823次

1.背景

(1)軟件開發過程中集合排序是比較強大的功能，會使用集合Map、Set、List實現排序功能，知道匿名內部類Comparator很關鍵，搞清楚集合排序的性能開銷，排序遇到的坑以及解決的方法，注意下面的例子都是JDK1.8的用法。

2.LIst集合排序

(1)UML類圖

(2)重點分析下ArrayList的排序，畢竟實戰開發用的最頻繁的就是它了

3.第一種做法

介紹：這種叫定制排序,或自定義排序,需編寫匿名內部類,先new一個Comparator接口的比較器對象c,同時實現compare()其方法;

然后將比較器對象c傳給Collections.sort()方法的參數列表中,實現排序功能;一般用這種的比較多。

(1)實體類(private int id)

public class Person{
    private int id;
    private String name;
    private String address; 
    public Person(int id, String name, String address) {
        this.id = id;
        this.name = name;
        this.address = address;
    } 
    public int getId() {
        return id;
    } 
    public void setId(int id) {
        this.id = id;
    } 
    public String getName() {
        return name;
    } 
    public void setName(String name) {
        this.name = name;
    } 
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    } 
    @Override
    public String toString() {
        return "Person{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

(2)測試類

public class ArrayListTest {
    public static void main(String[] args) {
        List<Person> list=Lists.newArrayList();
        //產生10以內的隨機數
        int num = (int)(Math.random()*1000+1);
        for(int i=num;i>0;i--){
            list.add(new Person(i,"張三","河南"));
        }
        for(Object o : list){
            System.out.println(o);
        }
        System.out.println("++++++++++++++++++++++++++++++++++++");
        Collections.sort(list, new Comparator<Person>() {
           @Override
           public int compare(Person o1, Person o2) {
               if (o1.getId() > o2.getId()) {
                   return 1;
               } else if (o1.getId() < o2.getId()) {
                   return -1;
               }
               return 0;
           }
       });
        for(Object o : list){
            System.out.println(o);
        }
    }
}

(3)結果(升序)

Person{id='10', name='張三', address='河南'}
Person{id='9', name='張三', address='河南'}
Person{id='8', name='張三', address='河南'}
Person{id='7', name='張三', address='河南'}
Person{id='6', name='張三', address='河南'}
Person{id='5', name='張三', address='河南'}
Person{id='4', name='張三', address='河南'}
Person{id='3', name='張三', address='河南'}
Person{id='2', name='張三', address='河南'}
Person{id='1', name='張三', address='河南'}
++++++++++++++++++++++++++++++++++++
Person{id='1', name='張三', address='河南'}
Person{id='2', name='張三', address='河南'}
Person{id='3', name='張三', address='河南'}
Person{id='4', name='張三', address='河南'}
Person{id='5', name='張三', address='河南'}
Person{id='6', name='張三', address='河南'}
Person{id='7', name='張三', address='河南'}
Person{id='8', name='張三', address='河南'}
Person{id='9', name='張三', address='河南'}
Person{id='10', name='張三', address='河南'}

4.第二中做法

(1)實體類(private String id)

public class Person{
    private String id;
    private String name;
    private String address; 
    public Person(String id, String name, String address) {
        this.id = id;
        this.name = name;
        this.address = address;
    } 
    public String getId() {
        return id;
    } 
    public void setId(String id) {
        this.id = id;
    } 
    public String getName() {
        return name;
    } 
    public void setName(String name) {
        this.name = name;
    } 
    public String getAddress() {
        return address;
    } 
    public void setAddress(String address) {
        this.address = address;
    } 
    @Override
    public String toString() {
        return "Person{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}

(2)測試類

public class ArrayListTest {
    public static void main(String[] args) {
        List<Person> list=Lists.newArrayList();
        //產生10以內的隨機數
        int num = (int)(Math.random()*100+1);
        for(int i=num;i>0;i--){
            list.add(new Person(""+i,"張三","河南"));
        }
        for(Object o : list){
            System.out.println(o);
        }
        System.out.println("++++++++++++++++++++++++++++++++++++");
       Collections.sort(list, new Comparator<Person>() {
           @Override
           public int compare(Person o1, Person o2) {
               return  new Double(o1.getId()).compareTo(new Double(o2.getId()));
           } 
       });
        for(Object o : list){
            System.out.println(o);
        }
    }
}

(3)結果

Person{id='10', name='張三', address='河南'}
Person{id='9', name='張三', address='河南'}
Person{id='8', name='張三', address='河南'}
Person{id='7', name='張三', address='河南'}
Person{id='6', name='張三', address='河南'}
Person{id='5', name='張三', address='河南'}
Person{id='4', name='張三', address='河南'}
Person{id='3', name='張三', address='河南'}
Person{id='2', name='張三', address='河南'}
Person{id='1', name='張三', address='河南'}
++++++++++++++++++++++++++++++++++++
Person{id='1', name='張三', address='河南'}
Person{id='2', name='張三', address='河南'}
Person{id='3', name='張三', address='河南'}
Person{id='4', name='張三', address='河南'}
Person{id='5', name='張三', address='河南'}
Person{id='6', name='張三', address='河南'}
Person{id='7', name='張三', address='河南'}
Person{id='8', name='張三', address='河南'}
Person{id='9', name='張三', address='河南'}
Person{id='10', name='張三', address='河南'}

5.第三種做法

另外一種稱為自然排序,參與排序的對象需實現comparable接口,重寫其compareTo()方法,方法體中實現對象的比較大小規則。

(1)實體類

public class Person implements Comparable{
    private String id;
    private String name;
    private String address; 
    public Person(String id, String name, String address) {
        this.id = id;
        this.name = name;
        this.address = address;
    } 
    public String getId() {
        return id;
    } 
    public void setId(String id) {
        this.id = id;
    } 
    public String getName() {
        return name;
    } 
    public void setName(String name) {
        this.name = name;
    } 
    public String getAddress() {
        return address;
    } 
    public void setAddress(String address) {
        this.address = address;
    } 
    @Override
    public String toString() {
        return "Person{" +
                "id='" + id + '\'' +
                ", name='" + name + '\'' +
                ", address='" + address + '\'' +
                '}';
    } 
    @Override
    public int compareTo(Object o) {
        if (o instanceof Person){
            Person o1 = (Person)o;
            return  new Double(this.getId()).compareTo(new Double(o1.getId()));
        }
        throw new ClassCastException("不能轉換為Person類型的對象...");
    }
}

(2)測試類

public class ArrayListTest {
    public static void main(String[] args) {
        List<Person> list=Lists.newArrayList();
        //產生10以內的隨機數
        int num = (int)(Math.random()*100+1);
        for(int i=num;i>0;i--){
            list.add(new Person(""+i,"張三","河南"));
        }
        for(Object o : list){
            System.out.println(o);
        }
        System.out.println("++++++++++++++++++++++++++++++++++++");
        Collections.sort(list);
        for(Object o : list){
            System.out.println(o);
        }
    }
}

(3)結果

Person{id='10', name='張三', address='河南'}
Person{id='9', name='張三', address='河南'}
Person{id='8', name='張三', address='河南'}
Person{id='7', name='張三', address='河南'}
Person{id='6', name='張三', address='河南'}
Person{id='5', name='張三', address='河南'}
Person{id='4', name='張三', address='河南'}
Person{id='3', name='張三', address='河南'}
Person{id='2', name='張三', address='河南'}
Person{id='1', name='張三', address='河南'}
++++++++++++++++++++++++++++++++++++
Person{id='1', name='張三', address='河南'}
Person{id='2', name='張三', address='河南'}
Person{id='3', name='張三', address='河南'}
Person{id='4', name='張三', address='河南'}
Person{id='5', name='張三', address='河南'}
Person{id='6', name='張三', address='河南'}
Person{id='7', name='張三', address='河南'}
Person{id='8', name='張三', address='河南'}
Person{id='9', name='張三', address='河南'}
Person{id='10', name='張三', address='河南'}

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Java中的各種集合排序

1.背景

2.LIst集合排序

3.第一種做法

4.第二中做法

5.第三種做法

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