TreeSet的两种排序方式
1.排序的引入
由于TreeSet可以实现对元素按照某种规则进行排序，例如下面的例子
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public class TreeSetDemo {
public static void main(String[] args) { TreeSet<Integer> ts =
new TreeSet<Integer>(); ts.add(
20); ts.add(
18); ts.add(
23); ts.add(
22); ts.add(
17); ts.add(
24); ts.add(
19); ts.add(
18); ts.add(
24);
for (Integer i : ts) { System.out.println(i); } } }
public class TreeSetDemo {
public static void main(String[] args) {
// 创建集合对象
// 自然顺序进行排序
TreeSet<Integer> ts = new TreeSet<Integer>();
// 创建元素并添加
// 20,18,23,22,17,24,19,18,24
ts.add(20);
ts.add(18);
ts.add(23);
ts.add(22);
ts.add(17);
ts.add(24);
ts.add(19);
ts.add(18);
ts.add(24);
// 遍历
for (Integer i : ts) {
System.out.println(i);
}
}
}
运行结果为：
但是对自定义对象呢？
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public class TreeSetDemo02 {
public static void main(String[] args) { TreeSet<Student> ts=
new TreeSet<Student>(); Student s1=
new Student(
“zhangsan”,
20); Student s2=
new Student(
“lis”,
22); Student s3=
new Student(
“wangwu”,
24); Student s4=
new Student(
“chenliu”,
26); Student s5=
new Student(
“zhangsan”,
22); Student s6=
new Student(
“qianqi”,
24); ts.add(s1); ts.add(s2); ts.add(s3); ts.add(s4); ts.add(s5); ts.add(s6);
for(Student s:ts){ System.out.println(s.getName()+
”———–”+s.getAge()); } } }
public class TreeSetDemo02 {
public static void main(String[] args) {
TreeSet<Student> ts=new TreeSet<Student>();
//创建元素对象
Student s1=new Student("zhangsan",20);
Student s2=new Student("lis",22);
Student s3=new Student("wangwu",24);
Student s4=new Student("chenliu",26);
Student s5=new Student("zhangsan",22);
Student s6=new Student("qianqi",24);
//将元素对象添加到集合对象中
ts.add(s1);
ts.add(s2);
ts.add(s3);
ts.add(s4);
ts.add(s5);
ts.add(s6);
//遍历
for(Student s:ts){
System.out.println(s.getName()+"-----------"+s.getAge());
}
}
}
Student类：
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public class Student {
private String name;
private int age;
public Student() {
super(); }
public Student(String name,
int age) {
super();
this.name = name;
this.age = age; }
public String getName() {
return name; }
public void setName(String name) {
this.name = name; }
public int getAge() {
return age; }
public void setAge(
int age) {
this.age = age; } }
public class Student {
private String name;
private int age;
public Student() {
super();
// TODO Auto-generated constructor stub
}
public Student(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
运行结果：
原因分析：
由于不知道该安照那一中排序方式排序，所以会报错。
解决方法：
1.自然排序
2.比较器排序
2.自然排序
自然排序要进行一下操作：
1.Student类中实现 Comparable<T>接口
2.重写Comparable接口中的Compareto方法
intcompareTo(T o) 比较此对象与指定对象的顺序。
故Student类为：
特别注意在重写Compareto方法时，注意排序
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package xfcy_04;
public class Student
implements Comparable<Student> {
private String name;
private int age;
public Student() {
super(); }
public Student(String name,
int age) {
super();
this.name = name;
this.age = age; }
public String getName() {
return name; }
public void setName(String name) {
this.name = name; }
public int getAge() {
return age; }
public void setAge(
int age) {
this.age = age; }
@Override public int compareTo(Student s) {
int num=
this.name.length()-s.name.length();
int num1=num==
0?
this.name.compareTo(s.name):num;
int num2=num1==
0?
this.age-s.age:num1;
return num2; } }
package xfcy_04;
/**
* Student类
* @author 晓风残月
*
*/
public class Student implements Comparable<Student> {
private String name;
private int age;
public Student() {
super();
// TODO Auto-generated constructor stub
}
public Student(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public int compareTo(Student s) {
//return -1; //-1表示放在红黑树的左边,即逆序输出
//return 1; //1表示放在红黑树的右边，即顺序输出
//return o; //表示元素相同，仅存放第一个元素
//主要条件 姓名的长度,如果姓名长度小的就放在左子树，否则放在右子树
int num=this.name.length()-s.name.length();
//姓名的长度相同，不代表内容相同,如果按字典顺序此 String 对象位于参数字符串之前，则比较结果为一个负整数。
//如果按字典顺序此 String 对象位于参数字符串之后，则比较结果为一个正整数。
//如果这两个字符串相等，则结果为 0
int num1=num==0?this.name.compareTo(s.name):num;
//姓名的长度和内容相同，不代表年龄相同，所以还要判断年龄
int num2=num1==0?this.age-s.age:num1;
return num2;
}
}
而主类中为：
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package xfcy_04;
import java.util.TreeSet;
public class TreeSetDemo02 {
public static void main(String[] args) { TreeSet<Student> ts=
new TreeSet<Student>(); Student s1=
new Student(
“zhangsan”,
20); Student s2=
new Student(
“lis”,
22); Student s3=
new Student(
“wangwu”,
24); Student s4=
new Student(
“chenliu”,
26); Student s5=
new Student(
“zhangsan”,
22); Student s6=
new Student(
“qianqi”,
24); ts.add(s1); ts.add(s2); ts.add(s3); ts.add(s4); ts.add(s5); ts.add(s6);
for(Student s:ts){ System.out.println(s.getName()+
”———–”+s.getAge()); } } }
package xfcy_04;
import java.util.TreeSet;
/*
* TreeSet存储自定义对象并保证排序和唯一。
*
* 需求：请按照姓名的长度排序
*/
public class TreeSetDemo02 {
public static void main(String[] args) {
//创建集合对象
TreeSet<Student> ts=new TreeSet<Student>();
//创建元素对象
Student s1=new Student("zhangsan",20);
Student s2=new Student("lis",22);
Student s3=new Student("wangwu",24);
Student s4=new Student("chenliu",26);
Student s5=new Student("zhangsan",22);
Student s6=new Student("qianqi",24);
//将元素对象添加到集合对象中
ts.add(s1);
ts.add(s2);
ts.add(s3);
ts.add(s4);
ts.add(s5);
ts.add(s6);
//遍历
for(Student s:ts){
System.out.println(s.getName()+"-----------"+s.getAge());
}
}
}
运行结果：
3、比较器排序
比较器排序步骤：
1.单独创建一个比较类，这里以MyComparator为例，并且要让其继承Comparator<T>接口
2.重写Comparator接口中的Compare方法
intcompare(T o1,T o2) 比较用来排序的两个参数。
3.在主类中使用下面的 构造方法
TreeSet(Comparator<? superE> comparator) 构造一个新的空 TreeSet，它根据指定比较器进行排序。
主类：
[java]
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package xfcy_04;
import java.util.TreeSet;
public class TreeSetDemo02 {
public static void main(String[] args) { TreeSet<Student> ts=
new TreeSet<Student>(
new MyComparator()); Student s1=
new Student(
“zhangsan”,
20); Student s2=
new Student(
“lis”,
22); Student s3=
new Student(
“wangwu”,
24); Student s4=
new Student(
“chenliu”,
26); Student s5=
new Student(
“zhangsan”,
22); Student s6=
new Student(
“qianqi”,
24); ts.add(s1); ts.add(s2); ts.add(s3); ts.add(s4); ts.add(s5); ts.add(s6);
for(Student s:ts){ System.out.println(s.getName()+
”———–”+s.getAge()); } } }
package xfcy_04;
import java.util.TreeSet;
/*
* TreeSet存储自定义对象并保证排序和唯一。
*
* 需求：请按照姓名的长度排序
*/
public class TreeSetDemo02 {
public static void main(String[] args) {
//创建集合对象
//TreeSet(Comparator<? super E> comparator) 构造一个新的空 TreeSet，它根据指定比较器进行排序。
TreeSet<Student> ts=new TreeSet<Student>(new MyComparator());
//创建元素对象
Student s1=new Student("zhangsan",20);
Student s2=new Student("lis",22);
Student s3=new Student("wangwu",24);
Student s4=new Student("chenliu",26);
Student s5=new Student("zhangsan",22);
Student s6=new Student("qianqi",24);
//将元素对象添加到集合对象中
ts.add(s1);
ts.add(s2);
ts.add(s3);
ts.add(s4);
ts.add(s5);
ts.add(s6);
//遍历
for(Student s:ts){
System.out.println(s.getName()+"-----------"+s.getAge());
}
}
}
MyComparator类：
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package xfcy_04;
import java.util.Comparator;
public class MyComparator
implements Comparator<Student>{
@Override public int compare(Student s1,Student s2) {
int num = s1.getName().length() - s2.getName().length();
int num2 = num ==
0 ? s1.getName().compareTo(s2.getName()) : num;
int num3 = num2 ==
0 ? s1.getAge() - s2.getAge() : num2;
return num3; } }
package xfcy_04;
import java.util.Comparator;
public class MyComparator implements Comparator<Student>{
@Override
public int compare(Student s1,Student s2) {
// 姓名长度
int num = s1.getName().length() - s2.getName().length();
// 姓名内容
int num2 = num == 0 ? s1.getName().compareTo(s2.getName()) : num;
// 年龄
int num3 = num2 == 0 ? s1.getAge() - s2.getAge() : num2;
return num3;
}
}
学生类（不需要继承Comparetable接口）
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package xfcy_04;
public class Student{
private String name;
private int age;
public Student() {
super(); }
public Student(String name,
int age) {
super();
this.name = name;
this.age = age; }
public String getName() {
return name; }
public void setName(String name) {
this.name = name; }
public int getAge() {
return age; }
public void setAge(
int age) {
this.age = age; } }
package xfcy_04;
/**
* Student类
* @author 晓风残月
*
*/
public class Student{
private String name;
private int age;
public Student() {
super();
// TODO Auto-generated constructor stub
}
public Student(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
}
运行结果：
4.比较器修改
由于单独创建一个类不是特别好，因而可以将MyComparetor的内容直接写到主类中
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public class TreeSetDemo {
public static void main(String[] args) { TreeSet<Student> ts =
new TreeSet<Student>(
new Comparator<Student>() {
@Override public int compare(Student s1, Student s2) {
int num = s1.getName().length() - s2.getName().length();
int num2 = num ==
0 ? s1.getName().compareTo(s2.getName()) : num;
int num3 = num2 ==
0 ? s1.getAge() - s2.getAge() : num2;
return num3; } }); Student s1 =
new Student(
“linqingxia”,
27); Student s2 =
new Student(
“zhangguorong”,
29); Student s3 =
new Student(
“wanglihong”,
23); Student s4 =
new Student(
“linqingxia”,
27); Student s5 =
new Student(
“liushishi”,
22); Student s6 =
new Student(
“wuqilong”,
40); Student s7 =
new Student(
“fengqingy”,
22); Student s8 =
new Student(
“linqingxia”,
29); ts.add(s1); ts.add(s2); ts.add(s3); ts.add(s4); ts.add(s5); ts.add(s6); ts.add(s7); ts.add(s8);
for (Student s : ts) { System.out.println(s.getName() +
”—” + s.getAge()); } } }
public class TreeSetDemo {
public static void main(String[] args) {
// 如果一个方法的参数是接口，那么真正要的是接口的实现类的对象
// 而匿名内部类就可以实现这个东西
TreeSet<Student> ts = new TreeSet<Student>(new Comparator<Student>() {
@Override
public int compare(Student s1, Student s2) {
// 姓名长度
int num = s1.getName().length() - s2.getName().length();
// 姓名内容
int num2 = num == 0 ? s1.getName().compareTo(s2.getName())
: num;
// 年龄
int num3 = num2 == 0 ? s1.getAge() - s2.getAge() : num2;
return num3;
}
});
// 创建元素
Student s1 = new Student("linqingxia", 27);
Student s2 = new Student("zhangguorong", 29);
Student s3 = new Student("wanglihong", 23);
Student s4 = new Student("linqingxia", 27);
Student s5 = new Student("liushishi", 22);
Student s6 = new Student("wuqilong", 40);
Student s7 = new Student("fengqingy", 22);
Student s8 = new Student("linqingxia", 29);
// 添加元素
ts.add(s1);
ts.add(s2);
ts.add(s3);
ts.add(s4);
ts.add(s5);
ts.add(s6);
ts.add(s7);
ts.add(s8);
// 遍历
for (Student s : ts) {
System.out.println(s.getName() + "---" + s.getAge());
}
}
}
运行结果也如同上面一样
5.总结
A:自然排序：要在自定义类中实现Comparerable<T>接口 ，并且重写compareTo方法
B:比较器排序：在自定义类中实现Comparetor<t>接口，重写
原文链接：http://blog.csdn.net/xiaofei__/article/details/53138681
