Some interview questions collected

Some interview questions collected

1. Define containers to store student information
   1) Find the oldest student in the class
   2) Find the information of the youngest classmate

import TreeMapDemo.Student;
import  Internal comparator _ External comparator .Emp;

import java.util.ArrayList;
import java.util.Comparator;
import java.util.TreeMap;

public class Example01 {
    
    public static void main(String[] args) {
    
        ArrayList<Student> list=new ArrayList();
        list.add(new Student(1001," Wang Xiaoer ",18," Zhang San "));
        list.add(new Student(1002," Wang Xiaosan ",19," Zhang San "));
        list.add(new Student(1003," Xiao Si Wang ",20," Zhang San "));
        list.add(new Student(1004," Wang Xiaowu ",21," Zhang San "));
        list.add(new Student(1005," Zhang San ",22," Zhang San "));
        // Anonymous inner class   Interface polymorphism 
           new Comparator<Student1>(){
    
               @Override
               public int compare(Student1 s1, Student1 s2) {
    
                   return s1.getAge()-s2.getAge();
               }
           };
        System.out.println(list);
        // Traverse 
        for(Student stu :list){
    
            System.out.println(stu.getAge());
        }
        System.out.println(" The oldest student in the class is ："+list.get(list.size()-1));
        System.out.println(" The youngest student in the class is ："+list.get(0));
    }
}

2. Simulated check-in ： Required HashMap Realization , You can add number check , time control
   1、 Prepare a blank notebook
   2、 Start checking in
   3、 Sign in end
   4、 Get how many people have signed in
   5、 Get all the lists
   6、 Check whether the monitor is on the list

import TreeMapDemo.Student;

import java.util.*;

/** *  Simulated check-in ：  Required ArrayList * 1、 Prepare a blank notebook  * 2、 Start checking in  * 3、 Sign in end  * 4、 Get how many people have signed in  * 5、 Get all the lists  * 6、 Check whether the monitor is on the list  * */
public class Example02 {
    
    public static void main(String[] args) {
    
        ArrayList<Student1> list=new ArrayList();
        HashMap<Integer,Student1> hm=new HashMap();
        // Check in Scanner simulation 
        Scanner sc=new Scanner(System.in);
        System.out.println("------------------ Start checking in --------------");
        //static long currentTimeMillis()  Returns the current time in milliseconds .  The returned data is a long integer 
        //Date​(long date)  Distribute  Date Object and initialize it to represent the self standard base time （ be called “ An era ”） Specified number of milliseconds since , namely 1970 year 1 month 1 Japan 00:00:00 GMT.
        /*boolean after(Date date)  If this method is called Date Object returns after the specified date true, Otherwise return to false */
// System.out.println(System.currentTimeMillis());
        Date end=new Date(System.currentTimeMillis()+120*1000);// Get the current time and the counted time 60 second 
        // Cycle sign in   Conditions for ending : 1) Enough people  2) It's time 
        while(true){
    
            System.out.println(" Please enter the registration number ：");
            int snum=sc.nextInt();
            System.out.println(" Please enter the student's name :");
            String name=sc.next();// Get the entered name 
            Student1 stu=new Student1(name,new Date());//new A store name and time Student class 
// list.add(stu);
            hm.put(snum,stu);
            // Number judgment 
            if(hm.size()==5){
    
                System.out.println(" Everyone has signed in ");
                break;
            }
            // The time limit 
            if(new Date().after(end)){
    
                System.out.println(" It's time , End sign in ");
                break;
            }
        }
        System.out.println(" Attendance "+hm.size());
        System.out.println(" Check in list "+hm);
       // Traverse map Assemble and judge whether monitor Zhang San is on the list 
        Set<Integer> set=hm.keySet();
        // To obtain a set aggregate , Use enhancements foreach and  Iterator
        Iterator it=set.iterator();// Get one Iterator object 
        while(it.hasNext()){
    
            if(hm.get(it.next()).getName().equals(" Zhang San ")){
    
                System.out.println(" Monitor Zhang San is on the list ！");
            }

        }

    }


}

3. character string 1234… Turn to one, two, three, four …

import java.util.HashMap;
import java.util.HashSet;
import java.util.Scanner;
import java.util.Set;

public class Example3 {
    
    public static void main(String[] args) {
    
        System.out.println(" Please enter the number you want to convert ：");
        Scanner sc=new Scanner(System.in);
        changUper(sc.next());
    }
  public static void changUper(String str){
    
      HashMap<Character,String> hm=new HashMap<>();
      hm.put('1'," one ");
      hm.put('2'," Ii. ");
      hm.put('3'," 3 ");
      hm.put('4'," boss ");
      hm.put('5'," wu ");
      hm.put('6'," lu ");
      hm.put('7'," Retailer, ");
      hm.put('8',"  ");
      hm.put('9'," nine ");
      hm.put('0'," zero ");
      String str1="";
      char[] chars=str.toCharArray();// Put the passed parameters str Convert to character array 
      Set<Character> set=hm.keySet();// Use HashMap Of keySet() Method 
      // Traverse 
      for(char  ch:chars){
    
       for (Character key:set){
    
           if(key.equals(ch)){
    
               // Put the traversal out key Value as parameter , Get the corresponding Value value , Then use string splicing 
               str1+=hm.get(key);

           }
       }
      }
      System.out.println(str1);
  }
}

4. One java The data is read from the file , Analyze the number of occurrences of each character , The results are stored in a file
   file : zhoumolahahaha,lazijiliaojieyixia,daimadoubuhuijiubiewanyouxila

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.HashMap;

/** *  One java The data is read from the file , Analyze the number of occurrences of each character , The results are stored in a file  *  file : zhoumolahahaha,lazijiliaojieyixia,daimadoubuhuijiubiewanyouxila * */
public class Example4 {
    
    public static void main(String[] args) throws IOException {
    
        recordCount();

    }
 public static void recordCount() throws IOException {
    
     FileReader fr=new FileReader("D://count.txt");
     FileWriter fw=new FileWriter("D://result.txt");
     int count=0;
     HashMap<Character,Integer> map=new HashMap<>();
     // Traversing the read file 
     while((count= fr.read())!= -1){
    //fr.read(), The number of characters read 
         char ch = (char)count;// Convert the received character wrapper class into characters 
         if(!map.containsKey(ch)){
    // Determine whether the set contains the key of this character , Add... If not included 
             map.put(ch,1);
         }else{
    // If it is included, it covers ,value It's worth it 1
             map.put(ch,map.get(ch) +1);
         }
         for(Character key : map.keySet()){
    
             fw.write(key + "="+ map.get(key) +"\t");
         };

     }
     fw.flush();
     fw.close();
     fr.close();

     }

}