String src = "12";
    int result = Integer.parseInt(src) + 22;
    System.out.println(result);

------解决方案--------------------
基础题，发一个全套的。
Java code

public final class Test {

    public static void main(String[] args) {
        
        String a = "12";
        int b = Integer.parseInt(a) + 22;
        System.out.println(b);
        
                
    }
}

------解决方案--------------------
boolean.parseBoolean(String s) 将字符串解析为boolean类型

Integer.parseInt(Sting s) 字符串参数作为有符号的十进制整数进行解析

double.parseDouble(String s) 返回一个新的 double 值，该值被初始化为用指定 String 表示的值

其他类型类似



------解决方案--------------------
在下一向不太爱走寻常路，这里也给个不寻常的解法吧：
Java code

public class Test2 {

    /**
     * @param args
     */
    public static void main(String[] args) {
        try {
            System.out.println(stringAdd("12", Integer.toString(22)));
            System.out.println(stringAdd("512", Integer.toString(699)));
        } catch (NumberFormatException ex) {
            System.out.println("字符串格式错误！");
        } catch (NullPointerException ex) {
            System.out.println("字符串未赋值！");
        }
    }

    static String stringAdd(String num1, String num2) {
        StringBuilder sbResult = new StringBuilder();
        int c = 0, index1 = num1.length() - 1, index2 = num2.length() - 1;

        if (notAnInteger(num1) || notAnInteger(num2))
            throw new NumberFormatException();

        while (index1 >= 0 || index2 >= 0) {
            char c1 = index1 >= 0 ? num1.charAt(index1) : '0';
            char c2 = index2 >= 0 ? num2.charAt(index2) : '0';
            char ch = (char) (c1 + c2 + c - '0');

            if (ch > '9') {
                c = 1;
                ch -= 10;
            } else
                c = 0;

            sbResult.insert(0, ch);
            index1--;
            index2--;
        }

        sbResult.insert(0, c > 0 ? "1" : "");

        return (sbResult.toString());
    }

    static boolean notAnInteger(String num) {
        for (int i = 0; i < num.length(); i++)
            if (num.charAt(i) < '0' || num.charAt(i) > '9')
                return (true);

        return (false);
    }
}

------解决方案--------------------
public final class Test {

   public static void main(String[] args) {
      
       String str = "12";
       int result = Integer.parseInt(str) + 22;
       System.out.println(result);
      
              
   }
}