本问介绍了Collections工具类两种sort()方法,具体如下:
一、Collections工具类两种sort()方法
格式一: public static <T extends Comparable<? super T>> void sort(List<T> list)
说明:该方法中的泛型<T>都是Comparable接口的子类,即只有是Comparable接口子类类型的数据,才能进行比较排序。如果其他类型的数据要进行比较排序,必须继承Comparable接口并
覆写equals()和compareTo()方法。其中如String类、Integer类都是Comparable接口子类,可以进行排序,而基本类型不能进行sort排序。比较项目在类内指定
格式二:public static <T> void sort(List<T> list, Comparator<? super T> c)
说明:该方法中指定比较方式Comparator<? super T> c,即c必须实现Comparator<? super T>接口,覆写compareTo()方法指定比较项目。比较项目在类外指定,比较灵活
二、示例
示例中获取字符串和数字的公用方法:
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/** * 生成随机 不重复的字符串 : number 生成字符串个数 */ public static List<String> generateString( int number) { List<String> listString = new ArrayList<>(); // 用于存放返回值 List<Integer> length = null ; // 字符串长度 StringBuffer sb = new StringBuffer(); // 中间变量 int control = 0 ; // 控制个数 String[] chars = new String[] { "a" , "b" , "c" , "d" , "e" , "f" , "g" , "h" , "i" , "j" , "k" , "l" , "m" , "n" , "o" , "p" , "q" , "r" , "s" , "t" , "u" , "v" , "w" , "x" , "y" , "z" , "0" , "1" , "2" , "3" , "4" , "5" , "6" , "7" , "8" , "9" , "A" , "B" , "C" , "D" , "E" , "F" , "G" , "H" , "I" , "J" , "K" , "L" , "M" , "N" , "O" , "P" , "Q" , "R" , "S" , "T" , "U" , "V" , "W" , "X" , "Y" , "Z" }; while ( true ) { // 控制结束 if ( control==number ) { break ; } // 生成随机数,生成36位的2aaab761-4341-4968-aceb-3861ee3824b2 UUID类型数据 String uuid = UUID.randomUUID().toString().replace( "-" , "" ); sb.setLength( 0 ); // 获得随机字符串长度,长度不为0 do { length = getDiffNo( 1 , 11 ); } while ( length.get( 0 )== 0 ); // 拼凑字符串 for ( int i= 0 ; i<length.get( 0 ); i++) { String str = uuid.substring(i* 3 , (i* 3 + 3 )); //将str字符串转换为16进制,获得其值 int x = Integer.parseInt(str, 16 ); //取余:x % 0x3E--0x3E = 3*16 + 14 = 62, 其中chars有62个字符 sb.append(chars[x % 0x3E ]); } listString.add(sb.toString()); control++; } return listString; } /** * 生成随机不重复的数字 :n生成个数 max生成范围 */ public static List<Integer> getDiffNo( int n, int max) { // 生成 [0-n] 个不重复的随机数 // list 用来保存这些随机数 List<Integer> list = new ArrayList<>(); Random random = new Random(); Integer k; for ( int i= 0 ; i<n; i++) { do { k = random.nextInt(max); } while (list.contains(k)); list.add(k); } return list; } |
1、对Integer泛型的List进行排序
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/** * 1.通过Collections.sort()方法,对Integer泛型的List进行排序; * 创建一个Integer泛型的List,插入十个100以内的不重复随机整数, 调用Collections.sort()方法对其进行排序 * 2.排序规则:先数字后字母,数字0-9,字母A-Z a-z的顺序 */ public void listIntegerSort() { // 插入十个100以内的不重复随机整数 List<Integer> integerList = getDiffNo( 10 , 100 ); System.out.println( "-------------排序前--------------" ); for (Integer integer : integerList) { System.out.println( "元素:" + integer); } Collections.sort(integerList); System.out.println( "----------------排序后-------------------" ); for (Integer integer : integerList) { System.out.println( "元素:" + integer); } } |
2、对String泛型的List进行排序
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/** * 1.对String泛型的List进行排序; 创建String泛型的List,添加乱序的String元素, * 调用sort方法,再次输出排序后的顺序 */ public void listStringSort() { List<String> stringList = new ArrayList<String>(); stringList.add( "eipJlcx" ); stringList.add( "WvQRufC" ); stringList.add( "J" ); stringList.add( "HdaU2G" ); stringList.add( "M0WswHD3" ); System.out.println( "------------排序前-------------" ); for (String string : stringList) { System.out.println( "元素:" + string); } Collections.sort(stringList); System.out.println( "--------------排序后---------------" ); for (String string : stringList) { System.out.println( "元素:" + string); } } |
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/** * 对String泛型的List进行排序,要求随机生成10个的不重复字符串,字符串的长度在10以内 */ public void listStringRandomSort() { // 生成随机字符串 List<String> listString = generateString( 10 ); System.out.println( "--------------排序前---------------" ); for (String integer : listString) { System.out.println( "元素:" + integer); } // 排序 Collections.sort(listString); System.out.println( "----------------排序后------------------" ); for (String integer : listString) { System.out.println( "元素:" + integer); } } |
3、对其他类型泛型的List进行排序
Course类实现
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/** * 课程类 * @author Administrator * */ public class Course { public String id; public String name; public Course(String id, String name) { this .id = id ; this .name = name; } public Course() { } @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 Course)) return false ; Course other = (Course) obj; if (name == null ) { if (other.name != null ) return false ; } else if (!name.equals(other.name)) return false ; return true ; } } |
Student类实现Comparable接口,类内设置比较项
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import java.util.HashSet; import java.util.Set; /** * 学生类 * @author Administrator * */ public class Student implements Comparable<Student> { public String id; public String name; public Set<Course> courses; public Student(String id, String name) { this .id = id; this .name = name; this .courses = new HashSet<Course>(); } @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 ; } @Override public int compareTo(Student o) { // 设置ID为比较项 // TODO Auto-generated method stub return this .id.compareTo(o.id); } } |
实现Comparator接口,类外设置比较项
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import java.util.Comparator; public class StudentComparator implements Comparator<Student> { @Override public int compare(Student o1, Student o2) { // TODO Auto-generated method stub return o1.name.compareTo(o2.name); } } |
比较Student类
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/** * 对其他类型泛型的List进行排序,以Student为例。 */ public void listComparatorSort() { List<Student> studentList = new ArrayList<Student>(); List<Integer> list = getDiffNo( 4 , 1000 ); studentList.add( new Student(list.get( 0 ) + "" , "Mike" )); studentList.add( new Student(list.get( 1 ) + "" , "Angela" )); studentList.add( new Student(list.get( 2 ) + "" , "Lucy" )); studentList.add( new Student( 1000 + "" , "Beyonce" )); System.out.println( "--------------排序前---------------" ); for (Student student : studentList) { System.out.println( "学生:" + student.id + ":" + student.name); } // 实现Comparator<T>接口,设置ID比较方式 Collections.sort(studentList); System.out.println( "----------------按照ID排序后------------------" ); for (Student student : studentList) { System.out.println( "学生:" + student.id + ":" + student.name); } // 实现Comparator<T>接口,设置特定比较方式,以name比较排序 Collections.sort(studentList, new StudentComparator()); System.out.println( "----------------按照姓名排序后-----------------" ); for (Student student : studentList) { System.out.println( "学生:" + student.id + ":" + student.name); } } |
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