Java-Collections工具类测试

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package collection;import java.util.*;public class CollectionsTest {    //通过Collections工具类中的sort方法对Integer泛型的List排序    public void testSort1()    {        List<Integer> integerList = new ArrayList<Integer>();        Random random = new Random();        Integer k;        for(int i = 0;i < 10;i++)        {            //通过nestInt()添加十个100内的不重复整数            k = random.nextInt(100);            if(integerList.contains(k) == false)            {                integerList.add(k);            }            System.out.println("成功添加整数："+k);        }        System.out.println("--------------排序前-------------");        for(Integer integer:integerList)        {            System.out.println(integer);        }        Collections.sort(integerList);        System.out.println("--------------排序后-------------");        for(Integer integer:integerList)        {            System.out.println(integer);        }    }    //通过Collections的sort方法对String泛型的List排序    public void testSort2()    {        List<String> stringList = new ArrayList<String>();        Random random = new Random();        //生成十条长度为10以内的随机字符串        String numbersAndLetters = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";        for(int i = 0;i < 10;i++)        {            int num = random.nextInt(10);            char[] ch = new char[num];            int k;            for(int j = 0;j < num;j++)            {                k = random.nextInt(62);                ch[j] = numbersAndLetters.charAt(k);            }            //将字符数组转化为字符串            StringBuffer sb = new StringBuffer();            for(int m = 0;m < ch.length;m++)            {                sb.append(ch[m]);            }            String newStr = sb.toString();            if(stringList.contains(newStr) == false && newStr.length() > 0)            {                stringList.add(newStr);            }            else            {                i--;            }        }        System.out.println("--------------排序前-------------");        for(String string:stringList)        {            System.out.println(string);        }        Collections.sort(stringList);        System.out.println("--------------排序后-------------");        for(String string:stringList)        {            System.out.println(string);        }    }    //对Student类型泛型的List排序    //Comparable接口：默认比较规则 Comparator接口：临时比较规则 对于一个对象不存在默认比较规则    public void testSort3()    {        List<Student> studentList = new ArrayList<Student>();        Random random = new Random();        //生成三个1000内的随机不重复ID        int k = 0;        int[] arr = new int[3];        while(k < 3)        {            boolean flag = true;             int rd = random.nextInt(1000);            for(int i = 0;i < k; i++)            {                if(arr[i]==rd)                {                    flag = false;                           }            }            if(flag)            {                arr[k] = rd;                k++;            }        }        studentList.add(new Student(arr[0]+"","Mike"));        studentList.add(new Student(arr[1]+"","Lucy"));        studentList.add(new Student(arr[2]+"","Jack"));        studentList.add(new Student(10000+"","Tom"));        System.out.println("--------------排序前-------------");        for(Student student:studentList)        {            System.out.println("学生："+student.id+":"+student.name);        }        Collections.sort(studentList);//要在Student类中实现Comparable接口        System.out.println("--------------按ID排序后-------------");        for(Student student:studentList)        {            System.out.println("学生："+student.id+":"+student.name);        }        Collections.sort(studentList,new StudentComparator());//重写comparator中的compare方法        System.out.println("--------------按姓名排序后-------------");        for(Student student:studentList)        {            System.out.println("学生："+student.id+":"+student.name);        }    }    public static void main(String[] args) {        CollectionsTest ct = new CollectionsTest();        //ct.testSort1();        //ct.testSort2();        ct.testSort3();    }}

package collection;import java.util.Comparator;public class StudentComparator implements Comparator<Student> {    @Override    //o1大于o2 返回正数    public int compare(Student o1, Student o2) {        return o1.name.compareTo(o2.name);    }}

package collection;import java.util.*;//学生类public class Student implements Comparable<Student> {    public String id;    public String name;    public Set<Course> courses;    @Override    public int hashCode() {        final int prime = 31;        int result = 1;        result = prime * result + ((name == null) ? 0 : name.hashCode());        return result;    }    @Override    public boolean equals(Object obj) {        if (this == obj)            return true;        if (obj == null)            return false;        if (!(obj instanceof Student))            return false;        Student other = (Student) obj;        if (name == null) {            if (other.name != null)                return false;        } else if (!name.equals(other.name))            return false;        return true;    }    public Student(String id,String name)    {        this.id = id;        this.name = name;        this.courses = new HashSet<Course>();    }    //按学生ID排序    @Override    public int compareTo(Student o) {        // 相等返回0 this对象较大返回正值 反之返回负值        return this.id.compareTo(o.id);    }}

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