java语言程序设计 第十版（基础篇）6.18

public static void main(String[] args) {
		// TODO Auto-generated method stub
		Scanner input = new Scanner(System.in);
    	System.out.print("Enter password:");
    	String password = input.next();
    	if(detectionString(password)){
    		System.out.println("Valid Password");
    	}
    	else
    		System.out.println("Invalid Password");

		
	}
	
	 
    public static boolean detectionString(String str){
    	if(str.length() < 8)
    		return false;
    	
    	int count = 0;
    	for(int i = 0; i < str.length(); ++i){
    		if(!Character.isDigit(str.charAt(i)) && !Character.isLetter(str.charAt(i)))
    			return false;
    		if(Character.isDigit(str.charAt(i)))
    			++count;
    	}
    	if(count < 2)
    		return false;
    	return true;
    }