float 不能直接做减法运算

			float a = 77.22f;
			float b = 77.2f;

			System.out.println((float)a-b);
			System.out.println((float)a+b);

			输出结果为：
			0.020004272
			154.42
		

		
package cn.netkiller.example;

import java.math.BigDecimal;

public class Math {

	public Math() {
		// TODO Auto-generated constructor stub
	}

	public static void main(String[] args) {

		float a = 77.22f;
		float b = 77.2f;

		System.out.println((float) a + b);
		System.out.println((float) a - b);
		System.out.println((float) a * b);
		System.out.println((float) a / b);

		System.out.println("-------------");

		System.out.println(add(a, b));
		System.out.println(sub(a, b));
		System.out.println(mul(a, b));
		System.out.println(div(a, b));

	}

	public static float add(float v1, float v2) {
		BigDecimal b1 = new BigDecimal(Float.toString(v1));
		BigDecimal b2 = new BigDecimal(Float.toString(v2));
		return b1.add(b2).floatValue();
	}

	public static float sub(float v1, float v2) {
		BigDecimal b1 = new BigDecimal(Float.toString(v1));
		BigDecimal b2 = new BigDecimal(Float.toString(v2));
		return b1.subtract(b2).floatValue();
	}

	public static float mul(float v1, float v2) {
		BigDecimal b1 = new BigDecimal(Float.toString(v1));
		BigDecimal b2 = new BigDecimal(Float.toString(v2));
		return b1.multiply(b2).floatValue();
	}

	public static float div(float v1, float v2) {
		return div(v1, v2, 5);
	}

	public static float div(float v1, float v2, int scale) {
		if (scale < 0) {
			throw new IllegalArgumentException("The scale must be a positive integer or zero");
		}
		BigDecimal b1 = new BigDecimal(Float.toString(v1));
		BigDecimal b2 = new BigDecimal(Float.toString(v2));
		return b1.divide(b2, scale, BigDecimal.ROUND_HALF_UP).floatValue();
	}

	public static float round(float v, int scale) {
		if (scale < 0) {
			throw new IllegalArgumentException("The scale must be a positive integer or zero");
		}
		BigDecimal b = new BigDecimal(Float.toString(v));
		BigDecimal one = new BigDecimal("1");
		return b.divide(one, scale, BigDecimal.ROUND_HALF_UP).floatValue();
	}
}