public class MathDemo {

public static void main(String[] args) {
    // 二進位制轉換十進位制 1100
    String num = "1100";
    // 拆分成字元陣列
    char[] ch = num.toCharArray();
    int total = 0;
    int[] number = new int[num.length()];
    int j = num.length() - 1;
    int totalNum=diGui(ch,total,number,j);
    System.out.println(totalNum);
}

public static int diGui(char[] ch, int total, int[] number, int j) {
    if (j >= 0) {
        for (int i = 0; i < ch.length; i++) {
            String s = ch[i] + "";
            number[i] = Integer.parseInt(s);// 1,1,0,0
            int temp = ((int) Math.pow(2, j));// 3,2,1,0 8
            total += number[i] * temp;// 1*8+
            //System.out.println(total);
              j--;
                diGui(ch, total, number, j);
            }
        }
          return total;
    }
}
 

新手一枚,寫的不好的地方還望指正。