字符串转换成整数

 public int StrToInt(String str) {
        char[] c = str.toCharArray();
        long sum = 0;
        int flag = 0;
        for(int i=0;i<=c.length-1;i++)
        {
            if(c[i]=='-'&&i==0)
            {
                flag = 1;
                continue;
            }
            if(c[i]=='+'&&i==0)
            {
                flag = 2;
                continue;
            }
            if(c[i]<'0'||c[i]>'9')
            {
                return 0;
            }
            else
            {
                sum = sum*10+c[i]-'0';
            }
        }
        if(flag==1)
        {
            long real = (-1)*sum;
            if(real<Integer.MIN_VALUE)
            {
                return 0;
            }
            return (int)real;
        }
        if(sum>Integer.MAX_VALUE)
        {
            return 0;
        }
        else{
            return (int) sum;
        }
    }