编写一个Java程序，递归地从一个文件中读取十个名字，然后依次输出名字中的字符总数、名字列表、名字列表。所有循环都必须递归执行。
Jay Walker
Erol Flintstone
C. Erol Madre
Billy Pilgrim
Mickey Angels
José Francisco de San Martín Squarebob
海绵裤
Mischa Ternoff
Chester Peak
Al Italia
Ben Dover
Pat Pending
我100%迷路了。我想建议从哪里开始。考虑到这个程序，我想构建一个主程序，它会调用一个首先读取文件的扫描仪。读取文件时，它会计算文本中的字符（快速提问，扫描仪会计算字符之间的空格吗？）。
接下来我想到了一个简单的打印函数，它可以显示整个names.txt文件。
最后，我迷失了 110% 的部分......我怎么会以相反的顺序列出名字？我会用什么？递归如何适应这一切？
递归部分的伪代码：
function printLines(lines):
if lines not empty:
print first line from lines // this prints lines in order
call printLines(remaining lines)
print first line again // this prints lines in reverse order
行的示例输出["line1", "line2", "line3"]
line1 // 1st output for printLines(["line1", "line2", "line3"])
line2 // 1st output for printLines(["line2", "line3"])
line3 // 1st output for printLines(["line3"])
// no output for printLines([])
line3 // 2nd output for printLines(["line3"])
line2 // 2nd output for printLines(["line2", "line3"])
line1 // 2nd output for printines(["line1", "line2", "line3"])
像这样的东西：
Reader(Stream strm)
{
string line;
if(!strm.eof())
{
line = strm.ReadLine();
Reader(strm);
}
// Info - char counte etc
string parseResult = Parse(line);
Print(parseResult);
}
递归将在文件末尾停止并开始展开。最后一条消息将首先打印。
您可以使用scanner.nextLine(). 它将读取包括空格在内的整行。
对于如何使用递归向后打印字符串，想象一下它是一种在侧面包含房屋的方式。您想向后参观房屋（尽管您进入了前进的方向）。所以你决定继续前进，直到路的尽头，然后一步一步地返回并打印邻居的房子名称。
function print( i )
if i == wayEnd
return
print(i + 1) // go ahead
// after you return, print:
output house at i
添加
方法的代码应该是：
private static Scanner scanner;
private static void readFile() {
if (!scanner.hasNext()) return;
String line = scanner.nextLine();
readFile();
System.out.println(line);
}
只需readFile()要从 main 调用：
public static void main(String[] args) {
scanner = new Scanner(new File("myText.txt"));
readFile();
}
为了训练我的 Java 技能，我为您编写了以下代码：
import java.util.*;
import java.io.*;
public class RecursiveReadNames{
public static final int MAXLINES = 10;
public static void main(String[] args) throws FileNotFoundException {
Scanner scan = new Scanner(new File("listOfNames.txt"));
String[] names = new String[MAXLINES];
readNames(names, scan, 0);
printNames(names,0);
System.out.println();
printNamesReverse(names,0);
System.out.println(totalNumberOfCharsInNames(names, 0,0));
}
static String[] readNames(String[] names, Scanner scan, int curLine) {
if(curLine >= MAXLINES)
return names;
names[curLine] = scan.nextLine();
return readNames(names, scan, curLine+1);
}
static void printNames(String[] names, int cur) {
if(cur >= names.length)
return;
System.out.println(names[cur]);
printNames(names, cur+1);
}
static void printNamesReverse(String[] names, int cur) {
if(cur >= names.length)
return;
printNamesReverse(names, cur+1);
System.out.println(names[cur]);
}
static int totalNumberOfCharsInNames(String[] names, int cur, int sum) {
if(cur >= names.length)
return sum;
return totalNumberOfCharsInNames(names, cur+1, sum+names[cur].length());
}
}
我不擅长扫描，但使用 Desolator 的扫描仪，您可以按如下方式完成其余部分，
private Scanner scanner;
static Map<String, Integer> counts = new HashMap<String, Integer>();
public static void main(String[] args) {
scanner = new Scanner(new File("myText.txt"));
readFile();
System.out.println(counts);
}
private void readFile() {
if (!scanner.hasNext()) return;
String line = scanner.nextLine();
String[] names = line.split("([\\W\\s]+)");
for(int i=0;i<names.length;i++) {
populateMap(names[i]);
}
readFile();
}
static void populateMap(String str) {
counts.put(reverse(str), str.length());
}
static String reverse(String s) {
if(s.length() == 0)
return "";
return s.charAt(s.length() - 1) + reverse(s.substring(0,s.length()-1));
}
做这样的事情
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.Scanner;
public class Test {
public static void printname(String name,BufferedReader br)
{
if(name!=null && br!=null)
{
try {
Test.printname(br.readLine(), br);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
System.out.println(name);
}
}
static Scanner scanner1 = new Scanner(System.in);
public static void main(String[] args)
{
//print the names and total character in each name
try {
FileInputStream fin=new FileInputStream("d:\\file.txt");
BufferedReader br=new BufferedReader(new InputStreamReader(fin));
String n;
while((n=br.readLine())!=null)
{
System.out.println(n+" length:"+n.length());
}
fin.close();
br.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
//print names in reverse order
try {
FileInputStream f=new FileInputStream("d:\\file.txt");
BufferedReader br=new BufferedReader(new InputStreamReader(f));
try {
Test.printname(br.readLine(),br);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
f.close();
br.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
注意我正在传递 br 对象
import java.util.Scanner;
import java.io.*;
class Listnames{
public static void recursiveRead(Scanner scanner) {
String name;
if(scanner.hasNext())
{name=scanner.next();
recursiveRead(scanner);
System.out.println(name.length() +" "+ name);
}
}
public static void main(String[] args)
{
try{
Scanner scanner=new Scanner(new File("name.txt"));
scanner.useDelimiter(System.getProperty("line.separator"));
recursiveRead(scanner);
}
catch (FileNotFoundException e) {
e.printStackTrace();
}
}
}