java格式化字符串的常用方法

package com.zhidi.tool;

import java.util.ArrayList;
import java.util.List;
import java.util.Random;

/**
 * 随机生成字符串或数字
 * @author Administrator
 *
 */
public class RandomDemo {
    
    /*
     * 随机生成一条字符串，长度通过参数传入
     */
    public static String getString(int len){
        
        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        Random ran = new Random();
        StringBuffer sb = new StringBuffer();
        
        for (int i = 0; i < len; i++) {
            char ch = str.charAt(ran.nextInt(str.length()));
            sb.append(ch);
        }
        
        return sb.toString();
    }
    
    /*
     * 随机生成字符串，长度不固定
     */
    public static String getString(){
        
        String str = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
        Random ran = new Random();
        StringBuffer sb = new StringBuffer();
        int len = ran.nextInt(10)+1;
        for (int i = 0; i < len; i++) {
            char ch = str.charAt(ran.nextInt(str.length()));
            sb.append(ch);
        }
        
        return sb.toString();
    }
    
    /*
     * 随机生成n条字符串，返回List<String>集合
     */
    public static List<String> getStringList(int len){
        List<String> list = new ArrayList<String>();
        
        for (int i = 0; i < len; i++) {
            String str = getString();
            list.add(str);
        }
        
        return list;
    }
    
    

}

package com.zhidi.tool;

import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;

public class ForString {

    
    /*
     * 清除重复字符，返回字符串
     */
    
    public String getString(String str){
        Set<Character> s = new HashSet<Character>();
        char[] ch = str.toCharArray();
        for (char c : ch) {
            s.add(c);
        }
        StringBuffer sb = new StringBuffer();
        
        for (char c : s) {
            sb.append(c);
        }
        
        return sb.toString();
    }
    
    /*
     * 返回重复的字符串
     */
    public String getCFString(String str){
        Set<Character> s = new HashSet<Character>();//清除重复的字符串
        Set<Character> s2 = new HashSet<Character>();//存放重复的字符串
        char[] ch = str.toCharArray();
        for (char c : ch) {
            boolean b = s.add(c);
            if(!b){
                s2.add(c);
            }
        }

        StringBuffer sb = new StringBuffer();
        for (char c : s2) {
            sb.append(c);
        }
        
        return sb.toString();
    }
    
    /*
     * 返回不重复的字符串
     */
    public String getNoCF(String str){
        Set<Character> s = new HashSet<Character>();//清除重复的字符串
        Set<Character> s2 = new HashSet<Character>();//存放重复的字符串
        Set<Character> s3 = new HashSet<Character>();//存放不重复的字符串
        char[] ch = str.toCharArray();
        for (char c : ch) {
            boolean b = s.add(c);
            if(!b){
                s2.add(c);
            }
        }
        
        s3.addAll(s);
        s3.removeAll(s2);

        StringBuffer sb = new StringBuffer();
        for (char c : s3) {
            sb.append(c);
        }
        
        return sb.toString();
    }
    
    /*
     * 返回Map集合，统计字符串中每个字符出现的次数
     */
    public Map<Character,Integer> getStringNum(String str){
        char[] ch = str.toCharArray();
        Map<Character,Integer> map = new HashMap<Character,Integer>();
        System.out.println(str);
        for (char c : ch) {
            if(map.containsKey(c)){
                Integer i = map.get(c);
                i++;
                map.put(c, i);
            }else{
                map.put(c, 1);
            }
        }
        return map;
    }
    
    
    
}

package com.zhidi;

import java.util.Collections;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
import java.util.Set;

import com.zhidi.tool.ForString;
import com.zhidi.tool.RandomDemo;

public class Test {

    public static void main(String[] args) {
    
//        List<String> list = RandomDemo.getStringList(10);
//        
//        Collections.sort(RandomDemo.getStringList(10));
//        for (String s : list) {
//            System.out.println(s);
//        }
        ForString fs = new ForString();
        Scanner sc = new Scanner(System.in);
        
        System.out.println("请输入一条字符串：");
        String str = sc.next();
        System.out.println(str);
        Map<Character, Integer> map = fs.getStringNum(str);
        System.out.println("------------------");
        Set<Character> s = map.keySet();
        for (Character c : s) {
            Integer i = map.get(c);
            System.out.println(c+"出现了"+i+"次");
        }
        
    }

}