Java 计算器实现

public class MyMath {
	public static final int DEFAULT_SCALE = 20;
	
	public static double add(double num1, double num2) {
		
		BigDecimal first = getBigDecimal(num1);
		BigDecimal second = getBigDecimal(num2);
		return first.add(second).doubleValue();
	}
	
	public static double substract(double num1, double num2) {
		
		BigDecimal first = getBigDecimal(num1);
		BigDecimal second = getBigDecimal(num2);
		return first.subtract(second).doubleValue();
	}
	
	public static double multiply(double num1, double num2) {
		
		BigDecimal first = getBigDecimal(num1);
		BigDecimal second = getBigDecimal(num2);
		return first.multiply(second).doubleValue();
	}
	
	public static double divide(double num1, double num2) {
		
		BigDecimal first = getBigDecimal(num1);
		BigDecimal second = getBigDecimal(num2);
		return first.divide(second,DEFAULT_SCALE, BigDecimal.ROUND_HALF_UP).doubleValue();
	}
	
	private static BigDecimal getBigDecimal(double num)
	{
		return new BigDecimal(num);
	}

}
public class MyMath {
	public st