1. BigDecimal num1 = new BigDecimal(2.225667);//这种写法不允许，会造成精度损失

2. BigDecimal num2 = new BigDecimal(2);//这种写法是可以的

3. BigDecimal num = new BigDecimal("2.225667");//一般都会这样写最好

4. int count = num.scale();

        System.out.println(count);//6 返回的是小数点后位数

好了，下面开始正式介绍知识点啦~~~~~~

1. ROUND_DOWN

BigDecimal b = new BigDecimal("2.225667").setScale(2, BigDecimal.ROUND_DOWN);
System.out.println(b);

2. ROUND_UP

BigDecimal c = new BigDecimal("2.224667").setScale(2, BigDecimal.ROUND_UP);
System.out.println(c);

3. ROUND_CEILING

天花板（向上），正数进位向上，负数舍位向上

BigDecimal f = new BigDecimal("2.224667").setScale(2, BigDecimal.ROUND_CEILING);
System.out.println(f);
BigDecimal g = new BigDecimal("-2.225667").setScale(2, BigDecimal.ROUND_CEILING);
System.out.println(g);

4. ROUND_FLOOR

地板（向下），正数舍位向下，负数进位向下

BigDecimal h = new BigDecimal("2.225667").setScale(2, BigDecimal.ROUND_FLOOR);
System.out.println(h);
BigDecimal i = new BigDecimal("-2.224667").setScale(2, BigDecimal.ROUND_FLOOR);
System.out.println(i);

5. ROUND_HALF_UP

BigDecimal d = new BigDecimal("2.225").setScale(2, BigDecimal.ROUND_HALF_UP);
System.out.println("ROUND_HALF_UP"+d); 

6. ROUND_HALF_DOWN

BigDecimal e = new BigDecimal("2.225").setScale(2, BigDecimal.ROUND_HALF_DOWN);
System.out.println("ROUND_HALF_DOWN"+e);

7. ROUND_HALF_EVEN

BigDecimal j = new BigDecimal("2.225").setScale(2, BigDecimal.ROUND_HALF_EVEN);
System.out.println(j);
BigDecimal k = new BigDecimal("2.215").setScale(2, BigDecimal.ROUND_HALF_EVEN);
System.out.println(k);
	System.out.println("************************************");
	System.out.println("4.05: "+new BigDecimal("4.05").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("4.15: "+new BigDecimal("4.15").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("4.25: "+new BigDecimal("4.25").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("4.35: "+new BigDecimal("4.35").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("4.45: "+new BigDecimal("4.45").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("4.55: "+new BigDecimal("4.55").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("4.65: "+new BigDecimal("4.65").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("3.05: "+new BigDecimal("3.05").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("3.15: "+new BigDecimal("3.15").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("3.25: "+new BigDecimal("3.25").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("3.35: "+new BigDecimal("3.35").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("3.45: "+new BigDecimal("3.45").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("3.55: "+new BigDecimal("3.55").setScale(1, BigDecimal.ROUND_HALF_EVEN));
	System.out.println("3.65: "+new BigDecimal("3.65").setScale(1, BigDecimal.ROUND_HALF_EVEN));

8.ROUND_UNNECESSARY

BigDecimal l = new BigDecimal("2.215").setScale(3, BigDecimal.ROUND_UNNECESSARY);
System.out.println(l);

原文地址:https://blog.csdn.net/qq_39101581/article/details/78624617