BigDecimal是不可变的，包括setScale（2，BigDecimal.ROUND_HALF_UP）在内的任何操作都会产生一个新的BigDecimal。正确的代码应该是

BigDecimal is immutable, any operation on it including setScale(2, BigDecimal.ROUND_HALF_UP) produces a new BigDecimal. Correct code should be

        BigDecimal bd = new BigDecimal(1);
//      bd.setScale(2, BigDecimal.ROUND_HALF_UP);   bd.setScale does not change bd
        bd = bd.setScale(2, BigDecimal.ROUND_HALF_UP);
        System.out.println(bd);

输出

1.00