直接上程式碼

public static void main(String[] args){
		Double a = 7.77;
		Double b = 3.33;
		System.out.println(a-b);
		System.out.println(new BigDecimal(a.toString()).subtract(new BigDecimal(b.toString())));
	}

    輸出結果

4.4399999999999995
4.44

使用BigDecimal承載資料的型別最好是String型別，否則依然會出現誤差

    同時附上加減乘除的方法

public static void main(String[] args){
		Double a = 7.77;
		Double b = 3.33;
		System.out.println(a-b);
		//加
		System.out.println(new BigDecimal(a.toString()).subtract(new BigDecimal(b.toString())));
		//減
		System.out.println(new BigDecimal(a.toString()).add(new BigDecimal(b.toString())));
		//乘
		System.out.println(new BigDecimal(a.toString()).multiply(new BigDecimal(b.toString())));
		//除
		///System.out.println(new BigDecimal(a.toString()).divide(new BigDecimal(b.toString())));
		System.out.println(new BigDecimal(a.toString()).divide(new BigDecimal(b.toString()),BigDecimal.ROUND_HALF_DOWN));
	}
 

注意在使用除法的時候，要指定舍入模式，否則在除不盡的情況下會報"Non-terminating decimal expansion; no exact representable decimal result"異常