java中的各种集合排序

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一、背景

1.软件开发过程中集合排序是比较强大的功能，会使用集合Map、Set、List实现排序功能，知道匿名内部类Comparator很关键，搞清楚集合排序的性能开销，排序遇到的坑以及解决的方法，注意下面的例子都是JDK1.8的用法。

二、LIst集合排序

1.UML类图

2.重点分析下ArrayList的排序，毕竟实战开发用的最频繁的就是它了

三、第一种做法

介绍：这种叫定制排序,或自定义排序,需编写匿名内部类,先new一个Comparator接口的比较器对象c,同时实现compare()其方法; 
然后将比较器对象c传给Collections.sort()方法的参数列表中,实现排序功能;一般用这种的比较多。

1.实体类（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.测试类

public class ArrayListTest {
    public static void main(String[] args) {
        List<Person> list=Lists.newArrayList();
        //产生10以内的随机数
        int num = (int)(Math.random()*1000+1);
        for(int i=num;i>0;i--){
            list.add(new Person(i,"张三","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.结果（升序）

Person{id='10', name='张三', address='河南'}
Person{id='9', name='张三', address='河南'}
Person{id='8', name='张三', address='河南'}
Person{id='7', name='张三', address='河南'}
Person{id='6', name='张三', address='河南'}
Person{id='5', name='张三', address='河南'}
Person{id='4', name='张三', address='河南'}
Person{id='3', name='张三', address='河南'}
Person{id='2', name='张三', address='河南'}
Person{id='1', name='张三', address='河南'}
++++++++++++++++++++++++++++++++++++
Person{id='1', name='张三', address='河南'}
Person{id='2', name='张三', address='河南'}
Person{id='3', name='张三', address='河南'}
Person{id='4', name='张三', address='河南'}
Person{id='5', name='张三', address='河南'}
Person{id='6', name='张三', address='河南'}
Person{id='7', name='张三', address='河南'}
Person{id='8', name='张三', address='河南'}
Person{id='9', name='张三', address='河南'}
Person{id='10', name='张三', address='河南'}

四、第二中做法

1.实体类（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.测试类

public class ArrayListTest {
    public static void main(String[] args) {
        List<Person> list=Lists.newArrayList();
        //产生10以内的随机数
        int num = (int)(Math.random()*100+1);
        for(int i=num;i>0;i--){
            list.add(new Person(""+i,"张三","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.结果

Person{id='10', name='张三', address='河南'}
Person{id='9', name='张三', address='河南'}
Person{id='8', name='张三', address='河南'}
Person{id='7', name='张三', address='河南'}
Person{id='6', name='张三', address='河南'}
Person{id='5', name='张三', address='河南'}
Person{id='4', name='张三', address='河南'}
Person{id='3', name='张三', address='河南'}
Person{id='2', name='张三', address='河南'}
Person{id='1', name='张三', address='河南'}
++++++++++++++++++++++++++++++++++++
Person{id='1', name='张三', address='河南'}
Person{id='2', name='张三', address='河南'}
Person{id='3', name='张三', address='河南'}
Person{id='4', name='张三', address='河南'}
Person{id='5', name='张三', address='河南'}
Person{id='6', name='张三', address='河南'}
Person{id='7', name='张三', address='河南'}
Person{id='8', name='张三', address='河南'}
Person{id='9', name='张三', address='河南'}
Person{id='10', name='张三', address='河南'}

五、第三种做法

另外一种称为自然排序,参与排序的对象需实现comparable接口,重写其compareTo()方法,方法体中实现对象的比较大小规则。

1.实体类

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("不能转换为Person类型的对象...");
    }
}

2.测试类

public class ArrayListTest {
    public static void main(String[] args) {
        List<Person> list=Lists.newArrayList();
        //产生10以内的随机数
        int num = (int)(Math.random()*100+1);
        for(int i=num;i>0;i--){
            list.add(new Person(""+i,"张三","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.结果

Person{id='10', name='张三', address='河南'}
Person{id='9', name='张三', address='河南'}
Person{id='8', name='张三', address='河南'}
Person{id='7', name='张三', address='河南'}
Person{id='6', name='张三', address='河南'}
Person{id='5', name='张三', address='河南'}
Person{id='4', name='张三', address='河南'}
Person{id='3', name='张三', address='河南'}
Person{id='2', name='张三', address='河南'}
Person{id='1', name='张三', address='河南'}
++++++++++++++++++++++++++++++++++++
Person{id='1', name='张三', address='河南'}
Person{id='2', name='张三', address='河南'}
Person{id='3', name='张三', address='河南'}
Person{id='4', name='张三', address='河南'}
Person{id='5', name='张三', address='河南'}
Person{id='6', name='张三', address='河南'}
Person{id='7', name='张三', address='河南'}
Person{id='8', name='张三', address='河南'}
Person{id='9', name='张三', address='河南'}
Person{id='10', name='张三', address='河南'}

六、结束

今天就写到这吧，太困了，晚安！各位，希望能帮到你们。

Always keep the faith!!!