java读书笔记-常用类-编程小问题

一、用Java编写一个程序，输出一个字符串中的大写英文字母数，小写英文字母数以及非英文字母数。

import java.util.regex.*;
public class TestString {
public static void main(String[] args) {
​
//方法一
//String s = "AaaaABBBBcc&^%adfsfdCCOOkk99876 _haHA";
//int lCount = 0, uCount = 0, oCount = 0;
/*
for(int i=0; i<s.length(); i++) {
char c = s.charAt(i);
if(c >= 'a' && c <= 'z') {
lCount ++;
} else if (c >='A' && c <= 'Z') {
uCount ++;
} else {
oCount ++;
}
}
*/

//方法二
/*
String sL = "abcdefghijklmnopqrstuvwxyz";
String sU = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
for(int i=0; i<s.length(); i++) {
char c = s.charAt(i);
if(sL.indexOf(c) != -1) {
lCount ++;
} else if (sU.indexOf(c) != -1) {
uCount ++;
} else {
oCount ++;
}
}
*/

//方法三
for(int i=0; i<s.length(); i++) {
char c = s.charAt(i);
if(Character.isLowerCase(c)) {
lCount ++;
} else if (Character.isUpperCase(c)) {
uCount ++;
} else {
oCount ++;
}
}

System.out.println(lCount + " " + uCount + " " + oCount);

二、将“1,2;3,4,5;6,7,8”这个字符串分解为二维数组。

public class ArrayParser {
public static void main(String[] args){
double[][] d;
String = "1,2;3,4,5;6,7,8";
String[] sFirst = s.split(";");
d = new double[sFirst.length][];
for(int i = 0; i < sFirst.length; i++){
String[] sSecond = sFirst[i].split(",");
d[i] = new double[sSecond.length];
for(int j = 0; j < sSecong.length; j++){
d[i][j] = Double.parseDouble(sSecond[j]);
}
}
for(int i = 0; i < d.length; i++){
for(int j = 0; j < d[i].length; j++){
System.out.print(d[i][j] + " ");
}
System.out.println();
}
}
}

三、利用递归列出目录结构

import java.io.*;
​
public class FileList {
public static void main(String[] args) {
File f = new File("d:/A");
System.out.println(f.getName());
tree(f, 1);
}
​
private static void tree(File f, int level) {
​
String preStr = "";
for(int i=0; i<level; i++) {
preStr += "    ";
}
​
File childs = f.listFiles();
for(int i=0; i<childs.length; i++) {
System.out.println(preStr + childs[i].getName());
if(childs[i].isDirectory()) {
tree(childs[i], level + 1);
}
}
}
}

四、编写一个方法，输出在一个字符串中，指定字符串出现的次数

String s = "sunjavahpjavaokjavajjavahahajavajavagoodjava";

String sToFind = "java";
int count = 0;
int index = -1;

while((index = s.indexOf(sToFind)) != -1) {
s = s.substring(index + sToFind.length());
count ++;
}

System.out.println(count);
​