集合第五发TreeSet和TreeMap

TreeSet和TreeMap

因为Tree是排序的，排序就要用到被排序元素的排序方法（compareTo（））而这个方法是comparable接口的抽象方法，因此使用TreeSet加入当中的元素必须实现该接口，然后实现compareTo方法。

TreeSet调用add方法是，会让新添加的元素调用compareTo方法，依次把已有的元素作为参数传入确定大小。

下面我们通过代码来具体理解：（PS：核心主要在对象的comparto方法中）

主类：

package cn.hncu.sort1;import java.util.Iterator;import java.util.TreeSet;public class TreeSetDemo {public static void main(String[] args) {TreeSet set=new TreeSet();Employee e1=new Employee("张三", 20);Employee e2=new Employee("李四", 21);Employee e3=new Employee("王五", 18);Employee e4=new Employee("赵六", 22);Employee e5=new Employee("李222", 21);set.add(e1);set.add(e2);set.add(e4);set.add(e3);set.add(e5);Iterator it=set.iterator();while(it.hasNext()){Employee ee=(Employee) it.next();System.out.println(ee);}}}

Employee类：

package cn.hncu.sort1;public class Employee implements Comparable{private String id;private String name;private int age;static int no=0;public Employee(String name, int age,String department) {super();this.id = id;this.name = name;this.age = age;id=""+(no++);}public Employee(String name, int age) {this(name,age,"none");}@Overridepublic int hashCode() {final int prime = 31;int result = 1;result = prime * result + age;result = prime * result + ((name == null) ? 0 : name.hashCode());return result;}@Overridepublic boolean equals(Object obj) {if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;Employee other = (Employee) obj;if (age != other.age)return false;if (name == null) {if (other.name != null)return false;} else if (!name.equals(other.name))return false;return true;}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 int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "Employee [id=" + id + ", name=" + name + ", age=" + age + "]";}//@Override//public int compareTo(Object o) {//return 1;//}@Overridepublic int compareTo(Object o) {if(o instanceof Employee){Employee e=(Employee) o;if (this.age!=e.age) {return this.age - e.age;}else{return this.id.compareTo(e.id);}}else if(o instanceof String){return 1;}return 0;}}

演示TreeMap的使用，我们通过第三方，new一个比较器传入TreeMap当中，这样我们的对象中就不要实现接口和写compareto方法了：

主类：

package cn.hncu.sort2;import java.util.Comparator;import java.util.Iterator;import java.util.Set;import java.util.TreeMap;import java.util.Map.Entry;import cn.hncu.sort2.Employee;public class Sort2Demo {public static void main(String[] args) {Employee e1=new Employee("张三", 20);Employee e2=new Employee("李四", 21);Employee e3=new Employee("王五", 18);Employee e4=new Employee("赵六", 22);Employee e5=new Employee("李222", 21);Comparator comparator=new MyCmp();TreeMap map =new TreeMap(comparator);map.put(e1, e1);map.put(e2, e2);map.put(e3, e3);map.put(e4, e4);map.put(e5, e5);Set entries =map.entrySet();Iterator it=entries.iterator();while(it.hasNext()){Entry entry=(Entry) it.next();System.out.println("key="+entry.getKey()+",value="+entry.getValue());}}}

Employee类（没有实现comparable接口和comparto方法的）：

package cn.hncu.sort2;//public class Employee implements Comparable{public class Employee {private String id;private String name;private int age;static int no=0;public Employee(String name, int age,String department) {super();this.id = id;this.name = name;this.age = age;id=""+(no++);}public Employee(String name, int age) {this(name,age,"none");}@Overridepublic int hashCode() {final int prime = 31;int result = 1;result = prime * result + age;result = prime * result + ((name == null) ? 0 : name.hashCode());return result;}@Overridepublic boolean equals(Object obj) {if (this == obj)return true;if (obj == null)return false;if (getClass() != obj.getClass())return false;Employee other = (Employee) obj;if (age != other.age)return false;if (name == null) {if (other.name != null)return false;} else if (!name.equals(other.name))return false;return true;}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 int getAge() {return age;}public void setAge(int age) {this.age = age;}@Overridepublic String toString() {return "Employee [id=" + id + ", name=" + name + ", age=" + age + "]";}//@Override//public int compareTo(Object o) {//return 1;//}//@Override//public int compareTo(Object o) {//if(o instanceof Employee){//Employee e=(Employee) o;////if (this.age!=e.age) {//return this.age - e.age;//}else{//return this.id.compareTo(e.id);//}//}else if(o instanceof String){//return 1;//}//return 0;////}}

Comparator（比较器）类：

package cn.hncu.sort2;import java.util.Comparator;public class MyCmp implements Comparator {@Overridepublic int compare(Object o1, Object o2) {Employee e1=(Employee) o1;Employee e2=(Employee) o2;return (e1.getId().compareTo(e2.getId()));}}

这里我还要将一个中文排序的问题

中文排序我们要用到一个Collator类。因为collator不好直接new对象，所以我们通过它的工厂方法来new。即：Collator collator=Collator.getInstance（）；然后拿collator.getcollationkey（）的返回值去比。

下面演示：

主类：

package cn.hncu.sort3;import java.util.Comparator;import java.util.Iterator;import java.util.Map.Entry;import java.util.Set;import java.util.TreeMap;public class Sort3Demo {public static void main(String[] args) {Comparator comparator=new MyCom2();TreeMap map=new TreeMap(comparator);map.put("张三", 10001);map.put("李四", 11111);map.put("王五", 12222);map.put("至死不渝", 1314258);Set entries=map.entrySet();Iterator it=entries.iterator();while(it.hasNext()){Entry entry=(Entry) it.next();System.out.println("key="+entry.getKey()+",value="+entry.getValue());}}}

Comparator（比较器）类：

package cn.hncu.sort3;import java.text.CollationKey;import java.text.Collator;import java.util.Comparator;public class MyCom2 implements Comparator{@Overridepublic int compare(Object o1, Object o2) {Collator collator=Collator.getInstance();CollationKey c1=collator.getCollationKey(o1.toString());CollationKey c2=collator.getCollationKey(o2.toString());return (c1.compareTo(c2));}}