Java String类练习题

题目：
1. 给定一个字符串,判断该字符串中是否包含某个子串.如果包含,求出子串的所有出现位置.
如:"abcbcbabcb34bcbd"中,"bcb"子串的出现位置为: 1,7,12.字符串和子串均由用户输入

2.给定一个长度,随机产生一个该长度的字符串,由大写,小写字母以及数字组成
Java中随机数的生成:
java.util.Random r = new java.util.Random();
int a = r.nextInt(100): a 0-99的随机数

3.给定一个由数字组成的字符串,如:"1239586838923173478943890234092",统计
出每个数字出现的次数

答案如下：

package Chp10;

import java.util.HashMap;
import java.util.Map;
import java.util.Random;
import java.util.Scanner;
import java.util.Set;

public class TestString2
{
	public static void Method_One()
	{
		
		Scanner s = new Scanner(System.in);
		System.out.println("请输入一个父串");
		String str = s.next();
		
		System.out.println("请输入一个子串");
		String str1 = s.next();
		
		int stat = 0;
		while (true)
		{
			int i = str.indexOf(str1,stat);
			if (i==-1)
			{
				break;
			}
			System.out.println(i);
			stat = i+str1.length();
		}
		
	}
	
	public static void Method_Two()
	{
		System.out.println("请输入一个长度");
		Scanner s = new Scanner(System.in);
		int n = s.nextInt();
		char[] cs = new char[n];
		
		Random random = new Random();
		for (int i = 0; i < n; i++)
		{
			int a = random.nextInt(62);
			if(a>=0 && a<=25)
			{
				a+=65;
			}
			else if (a>25 && a<=51) 
			{
				// 97 - 26 = 71
				a+=71;
			}
			else 
			{
				// 52-48 = 4
				a-=4;
			}
			cs[i] = (char)a;
		}
		System.out.println(cs);
	}
	
	public  static void  Method_Three()
	{
		Scanner scanner = new Scanner(System.in);
		String string = scanner.next();
		int[] c = new int[10];
		for (int i = 0; i < string.length(); i++)
		{
			char c1 = string.charAt(i); //48-57
			int a = c1-48;	// 类型转换
			c[a]++;
		}
		for (int i = 0; i < c.length; i++)
		{
			System.out.println(i+" 出现的次数： "+c[i]);
		}
		
		System.out.println("=========方法二==========");
		String s = "12548954231351486214894562";
		char[] ch = s.toCharArray();
		
		Map<Character, Integer> map = new HashMap<Character, Integer>();
		Set<Character> set = map.keySet();
		for (int i = 0; i < ch.length; i++)
		{
			if (set.contains(ch[i])) // 判断map中已经有的char值
			{
				map.put(ch[i], map.get(ch[i])+1);
			} else
			{
				map.put(ch[i], 1); // 第一次放入map中
			}
		}
		Set<Character> set2 = map.keySet();
		for (Character character : set2)
		{
			System.out.println(character+"=========="+map.get(character));
		}
	}
	
	public static void main(String[] args)
	{
		System.out.println("第一题如下:");
		Method_One();
		System.out.println("第二题如下:");
		Method_Two();
		System.out.println("第三题如下:");
		Method_Three();
	}
}