TreeSet是Set集合的常見子類.

TreeSet:底層結(jié)構(gòu)是 二叉樹

　　　　元素是有排序的,但是不可以有重復(fù)元素.

相關(guān)代碼演練:

/*TreeSet ;元素是有序的,但是不可以元素重復(fù).                    */import java.util.*;class TreeSetDemo{    public static void main(String [] args)    {        TreeSet ts = new TreeSet();                ts.add("java01");        ts.add("java03");        ts.add("java02");        ts.add("java04");        ts.add("java04");                Iterator it = ts.iterator();                while(it.hasNext())        {            sop(it.next());        }                ts.remove("java02");        sop(ts);            }    public static void sop(Object obj)    {        System.out.PRintln(obj);    }        }class Student{    private String name;    private int age;        Student(String name,int age)    {        this.name = name;        this.age = age;    }        public String getName()    {        return name;    }    public int getAge()    {        return age;    }}

TreeSet的兩種排序方式:第一種排序方式:(讓元素自身具備比較性)讓該類實(shí)現(xiàn)Comparable接口.并且覆寫compareTo方法.這種排序是自然排序.

　　　　　　　保證元素唯一性的依據(jù)是: compareTo方法return 0;

代碼演示:

/*        TreeSet存儲(chǔ)自定義對(duì)象                (會(huì)拋出類型轉(zhuǎn)換異常ClassCastException) Student類無法轉(zhuǎn)成Comparable.        因此Student類需要實(shí)現(xiàn)Comparable接口.并且覆寫compareTo方法.排序的方式為自然順序.                排序時(shí),當(dāng)主要條件相同時(shí),還要判斷一下次要條件.                        需求: 按學(xué)生的年齡排序.*/import java.util.*;class TreeSetTest{    public static void main(String [] args)    {        TreeSet ts = new TreeSet();                ts.add(new Student("lisi08",19));        ts.add(new Student("lisi02",22));        ts.add(new Student("lisi007",20));        ts.add(new Student("lisi09",19));                        Iterator it = ts.iterator();                while(it.hasNext())        {            Student stu = (Student)it.next();            sop(stu.getName()+"------"+stu.getAge());        }            }    public static void sop(Object obj)    {        System.out.println(obj);    }    }class Student implements Comparable //該接口強(qiáng)制讓學(xué)生具備了比較性. (實(shí)現(xiàn)了該接口需要覆蓋其compareTo方法){    private String name;    private int age;        Student(String name,int age)    {        this.name = name;        this.age = age;    }    public int compareTo(Object obj)    {                //return 1; //怎么存的怎么取出        //return -1;  //倒取存入的對(duì)象        //return 0;        //只會(huì)存入第一個(gè)存入的對(duì)象.                if(!(obj instanceof Student))            throw new RuntimeException("不是學(xué)生對(duì)象");                    Student s = (Student)obj;                System.out.println(this.name+"---compareTo---"+s.name);                if(this.age>s.age)            return 1;        if(this.age==s.age)        {            return this.name.compareTo(s.name);        }        return -1;            }                public String getName()    {        return name;    }    public int getAge()    {        return age;    }}

第二種排序方式:(元素不具備比較性,或者比較性是所不需要的)此時(shí),讓集合自身具備比較性.在集合一初始化時(shí),就有比較方式.實(shí)現(xiàn)方式: 定義一個(gè)類,實(shí)現(xiàn)comparator接口,并覆寫其中的compare方法.

/*讓容器自身具備比較性,定義一個(gè)比較器.將比較器對(duì)象傳遞給TreeSet集合的構(gòu)造函數(shù);思路步驟:定義一個(gè)容器讓這個(gè)容器實(shí)現(xiàn)comparator,并且覆寫其中的compare方法.*/import java.util.*;class TreeSetTest2{    public static void main(String [] args)    {        //TreeSet ts = new TreeSet(); //傳入的不是比較器對(duì)象時(shí),調(diào)用的是CompareTo方法.                TreeSet ts = new TreeSet(new MyComparator());  //將比較器傳遞給TreeSet的構(gòu)造函數(shù).                ts.add(new Student("lisi08",19));        ts.add(new Student("lisi02",22));        ts.add(new Student("lisi02",23));        ts.add(new Student("lisi007",20));        ts.add(new Student("lisi09",19));                Iterator it = ts.iterator();                while(it.hasNext())        {            Student stu = (Student)it.next();            sop(stu.getName()+"-----"+stu.getAge());        }                    }        public static void sop(Object obj)    {        System.out.println(obj);    }        }class Student implements Comparable //讓學(xué)生類具備了比較性{    private String name;    private int age;    Student(String name,int age)    {        this.name = name;        this.age = age;    }    public String getName()    {        return name;    }    public int getAge()    {        return age;    }        public int compareTo(Object obj)  //覆寫了Comparable中的compareTo方法.    {        if(!(obj instanceof Student))            throw new RuntimeException("bushixueshengduixiang");                Student s = (Student)obj;        if(this.age>s.age)            return 1;        if(this.age==s.age)        {            return this.name.compareTo(s.name);        }        return -1;    }}class MyComparator implements Comparator  //定義一個(gè)容器并實(shí)現(xiàn)了Comparator接口{    public int compare(Object o1,Object o2)  //覆寫其中的compare方法.    {                if(!(o1 instanceof Student ||o2 instanceof Student))            throw new RuntimeException("對(duì)象錯(cuò)誤.");                Student s1 = (Student)o1;        Student s2 = (Student)o2;                //return s1.getName().compareTo(s2.getName()); //無法存儲(chǔ)到姓名相同年齡不同的對(duì)象.                int num = s1.getName().compareTo(s2.getName());  //判斷返回值 (1 0 -1)        if(num==0)   //判斷的名字相同時(shí),在判斷其年齡是否相同.        {            return s1.getAge()-s2.getAge();            /*            if(s1.getAge()>s2.getAge())                return 1;            if(s1.getAge()==s2.getAge())                return 0;            return -1;            */        }                return num;            }}

練習(xí):

按照字符串的長(zhǎng)度進(jìn)行排序.

/*練習(xí):按照字符串長(zhǎng)度排序*/import java.util.*;class TreeSetExam{    public static void main(String [] args)    {        TreeSet ts = new TreeSet(new StrLengthCompare());                    ts.add("abcd");        ts.add("cc");        ts.add("cba");        ts.add("a");        ts.add("hahaha");        ts.add("aa");                Iterator it = ts.iterator();                while(it.hasNext())        {            sop(it.next());        }            }        public static void sop(Object obj)    {        System.out.println(obj);    }    }class StrLengthCompare implements Comparator{    public int compare(Object o1,Object o2)    {        if(!(o1 instanceof String || o2 instanceof String))            throw new RuntimeException("ERROR");                String s1 = (String)o1;        String s2 = (String)o2;                //int num = s1.length()-s2.length();        int num = new Integer(s1.length()).compareTo(new Integer(s2.length()));                if(num==0) //判斷長(zhǎng)度一樣的字符串的自然排序.        {            return s1.compareTo(s2);        }        return num;    }}

注意:一定要記得先對(duì)主要條件進(jìn)行判斷,在對(duì)次要條件進(jìn)行判斷.避免出現(xiàn)漏存的情況.