"Prove safety offer" 11 questions face value of a power of Java version

The book Methods: This question is to be noted that base number is zero. type double equivalence determination. Power recursive algorithm.

    public double power(double base, int exponent){
        //指数为0
         if(exponent == 0){
            return 1.0;
        }
        //底数为0
        if(isEqual(base, 0.0)){
            return 0.0;
        }
        
        int absExponent = exponent;
        if(exponent < 0)absExponent = -absExponent;
        
        double result = unsignedPower(base, absExponent);
        
        if(exponent<0){
            result = 1.0/result;
        }
        
        return result;
    }
    //求乘方正常思路
    private double unsignedPower(double base, int absExponent){
        double result = 1.0;
        for(int i=1; i<=absExponent; i++){
            result *= base;
        }
        return result;
    }
    //用递归的方法求乘方
    private double unsignedPower2(double base, int absExponent){
        if(absExponent == 1)return base;
        double result = unsignedPower2(base, absExponent>>1);
        result *= result;
        if((absExponent & 0x01) == 1){
            result *= base;
        }
        return result;
    }
    //double类型判断相等
    private boolean isEqual(double num1, double num2){
        if((num1 - num2)>-0.0000001 && (num1 - num2)<0.0000001){
            return true;
        }else{
            return false;
        }
    }