随机生成5位大小写字母或者数字_随机生成5个字母

随机生成5位大小写字母或者数字

方法一：生成不重复的

public static void main(String[] args) {
		Random rand = new Random();
		char[] letters=new char[]{'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q',
				'R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i',
				'j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','r',
				'0','1','2','3','4','5','6','7','8','9'};
		String str = "";
		int index;
		boolean[] flags = new boolean[letters.length];//默认为false
		for(int i=0;i<5;i++){
			do{
				index = rand.nextInt(letters.length); 
			}while(flags[index]==true);
			char c = letters[index];
			str += c;
			flags[index]=true;
		}
		System.out.println(str);
	}

方法二：生成重复的，与方法一类似

public static void main(String[] args) {
		Random rand = new Random();
		char[] letters=new char[]{'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q',
				'R','S','T','U','V','W','X','Y','Z','a','b','c','d','e','f','g','h','i',
				'j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z','r',
				'0','1','2','3','4','5','6','7','8','9'};
		String str = "";
		int index;
		boolean[] flags = new boolean[letters.length];//默认为false
		for(int i=0;i<5;i++){
			do{
				index = rand.nextInt(letters.length); 
			}while(flags[index]==true);
			char c = letters[index];
			str += c;
			flags[index]=true;
		}
		System.out.println(str);
	}

方法三：生成重复的（建议选用此方法）

public static void main(String[] args) {
		String str = "";
		Random rand = new Random();
		for(int i=0;i<5;i++){
			int num = rand.nextInt(3);
			switch(num){
				case 0:
					char c1 = (char)(rand.nextInt(26)+'a');//生成随机小写字母 
					str += c1;
					break;
				case 1:
					char c2 = (char)(rand.nextInt(26)+'A');//生成随机大写字母 
					str += c2;
					break;
				case 2:
					str += rand.nextInt(10);//生成随机数字
			}
		}
		System.out.println("生成的5个随机验证码是:"+str);
	}