String忽略大小写方法compareToIgnoreCase源码及Comparator自定义比较器
//源码 public int compareToIgnoreCase(String str) { return CASE_INSENSITIVE_ORDER.compare(this, str); } /** * A Comparator that orders {@code String} objects as by * {@code compareToIgnoreCase}. This comparator is serializable. * <p> * Note that this Comparator does <em>not</em> take locale into account, * and will result in an unsatisfactory ordering for certain locales. * The java.text package provides <em>Collators</em> to allow * locale-sensitive ordering. * * @see java.text.Collator#compare(String, String) * @since 1.2 */ public static final Comparator<String> CASE_INSENSITIVE_ORDER = new CaseInsensitiveComparator(); private static class CaseInsensitiveComparator implements Comparator<String>, java.io.Serializable { // use serialVersionUID from JDK 1.2.2 for interoperability private static final long serialVersionUID = 8575799808933029326L; public int compare(String s1, String s2) { int n1 = s1.length(); int n2 = s2.length(); int min = Math.min(n1, n2); for (int i = 0; i < min; i++) { char c1 = s1.charAt(i); char c2 = s2.charAt(i); if (c1 != c2) { c1 = Character.toUpperCase(c1); c2 = Character.toUpperCase(c2); if (c1 != c2) { c1 = Character.toLowerCase(c1); c2 = Character.toLowerCase(c2); if (c1 != c2) { // No overflow because of numeric promotion return c1 - c2; } } } } return n1 - n2; } /** Replaces the de-serialized object. */ private Object readResolve() { return CASE_INSENSITIVE_ORDER; } }
对于设置的比较器的升序和降序问题的解释
public interface Comparator<T>{
int compare(T first, T second);
}
通过计算两个字符串,如果第一个参数大于第二个参数,则返回一个正数,反之则返回一个负数
当返回结果为负数时,表示不需要交换两个参数的位置
当返回结果为正数时,表示需要交换两个参数的位置
而当数组进行排序时,从前往后传入两个参数,传入无非两种情况:
第一个参数大于第二个参数–>返回值为正数–>交换两个参数
第一个参数小于第二个参数–>返回值为负数–>不交换两个参数
我们会发现,这两种结果其实都指向一个相同的结论,就是执行完都会使得第一个参数小于第二个参数,故符合开始的结论:return first.a - second.a表示按升序排序
那么自然如果return second.a -first.a则表示按降序排序。
//DEMO public class Student implements Comparable<Student>{ /** * 姓名 */ private String username; /** * 年龄 */ private int age; public Student() { super(); } public Student(String username, int age) { this.username = username; this.age = age; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } @Override public int compareTo(Student o) { return this.age-o.age;//升序 } } package com.example.core.mydemo.json; import com.alibaba.fastjson.JSON; import com.example.core.mydemo.json.vo.Student; import java.util.*; import java.util.stream.Collectors; public class ComparatorTest { public static void main(String[] args) { Student s1 = new Student("Aliming",8); Student s2 = new Student("ajiaqi",9); Student s3 = new Student("Bruixing",7); Student s4 = new Student("bzeyi",7); List<Student> list = new ArrayList(); list.add(s1); list.add(s2); list.add(s3); list.add(s4); int size = list.size(); List<String> listTmp = list.stream().map(Student::getUsername).collect(Collectors.toList()); String [] arrayToSort = listTmp.toArray(new String[size]); // Arrays.sort(arrayToSort, String.CASE_INSENSITIVE_ORDER); //忽略大小写 Arrays.sort(arrayToSort); //默认是区分大小写 /** * 区分大小写 * 排序1:Aliming * 排序1:Bruixing * 排序1:ajiaqi * 排序1:bzeyi * * * 忽略大小写 * 排序1:ajiaqi * 排序1:Aliming * 排序1:Bruixing * 排序1:bzeyi * */ for(int i = 0; i < size; i ++) { System.out.println(" 排序1:" + arrayToSort[i]); } List<String> featureSort = listTmp.stream().sorted((a,b) -> (a.compareToIgnoreCase(b))).collect(Collectors.toList()); for(int i = 0; i < size; i ++) { System.out.println(" 排序2:" + arrayToSort[i]); } Collections.sort(list, new Comparator<Student>() {//比较器 @Override public int compare(Student o1, Student o2) { // return o2.getAge()-o1.getAge();//以学生的年龄降序 return o1.getAge()-o2.getAge();//以学生的年龄升序 } }); /** * 排序3:{"age":7,"username":"Bruixing"} * 排序3:{"age":7,"username":"bzeyi"} * 排序3:{"age":8,"username":"Aliming"} * 排序3:{"age":9,"username":"ajiaqi"} */ for (int i = 0; i < list.size(); i++) { System.out.println("排序3:" + JSON.toJSONString(list.get(i))); } Collections.sort(list, new Comparator<Student>() { @Override public int compare(Student o1, Student o2) { // 年龄降序 int result = o2.getAge()-o1.getAge();//年龄降序 if(result==0){//第一个规则判断完了 下一个规则 姓名的首字母 升序 result = o1.getUsername().charAt(0)-o2.getUsername().charAt(0); } return result; } }); /** * 排序4:{"age":9,"username":"ajiaqi"} * 排序4:{"age":8,"username":"Aliming"} * 排序4:{"age":7,"username":"Bruixing"} * 排序4:{"age":7,"username":"bzeyi"} */ for (int i = 0; i < list.size(); i++) { System.out.println("排序4:" + JSON.toJSONString(list.get(i))); } } }
标签:String,自定义,int,age,源码,Student,排序,public From: https://www.cnblogs.com/oktokeep/p/16769126.html