import java.math.BigDecimal;public class TestGetInt {    public static void main(String[] args) {        double i = 2, j = 2.1, k = 2.5, m = 2.9;        System.out.println("舍掉小数取整:Math.floor(2)=" + (int) Math.floor(i));//2        System.out.println("舍掉小数取整:Math.floor(2.1)=" + (int) Math.floor(j));//2        System.out.println("舍掉小数取整:Math.floor(2.5)=" + (int) Math.floor(k));//2        System.out.println("舍掉小数取整:Math.floor(2.9)=" + (int) Math.floor(m));//2        System.out.println("四舍五入取整:(2)=" + new BigDecimal("2").setScale(0, BigDecimal.ROUND_HALF_UP));//2        System.out.println("四舍五入取整:(2.1)=" + new BigDecimal("2.1").setScale(0, BigDecimal.ROUND_HALF_UP));//2        System.out.println("四舍五入取整:(2.5)=" + new BigDecimal("2.5").setScale(0, BigDecimal.ROUND_HALF_UP));//3        System.out.println("四舍五入取整:(2.9)=" + new BigDecimal("2.9").setScale(0, BigDecimal.ROUND_HALF_UP));//3        System.out.println("凑整:Math.ceil(2)=" + (int) Math.ceil(i));//2        System.out.println("凑整:Math.ceil(2.1)=" + (int) Math.ceil(j));//3        System.out.println("凑整:Math.ceil(2.5)=" + (int) Math.ceil(k));//3        System.out.println("凑整:Math.ceil(2.9)=" + (int) Math.ceil(m));//3        System.out.println("舍掉小数取整:Math.floor(-2)=" + (int) Math.floor(-i));//-2        System.out.println("舍掉小数取整:Math.floor(-2.1)=" + (int) Math.floor(-j));//-3        System.out.println("舍掉小数取整:Math.floor(-2.5)=" + (int) Math.floor(-k));//-3        System.out.println("舍掉小数取整:Math.floor(-2.9)=" + (int) Math.floor(-m));//-3        System.out.println("四舍五入取整:(-2)=" + new BigDecimal("-2").setScale(0, BigDecimal.ROUND_HALF_UP));//-2        System.out.println("四舍五入取整:(-2.1)=" + new BigDecimal("-2.1").setScale(0, BigDecimal.ROUND_HALF_UP));//-2        System.out.println("四舍五入取整:(-2.5)=" + new BigDecimal("-2.5").setScale(0, BigDecimal.ROUND_HALF_UP));//-3        System.out.println("四舍五入取整:(-2.9)=" + new BigDecimal("-2.9").setScale(0, BigDecimal.ROUND_HALF_UP));//-3        System.out.println("凑整:Math.ceil(-2)=" + (int) Math.ceil(-i));//-2        System.out.println("凑整:Math.ceil(-2.1)=" + (int) Math.ceil(-j));//-2        System.out.println("凑整:Math.ceil(-2.5)=" + (int) Math.ceil(-k));//-2        System.out.println("凑整:Math.ceil(-2.9)=" + (int) Math.ceil(-m));//-2    }}

结果

舍掉小数取整:Math.floor(2)=2舍掉小数取整:Math.floor(2.1)=2舍掉小数取整:Math.floor(2.5)=2舍掉小数取整:Math.floor(2.9)=2四舍五入取整:(2)=2四舍五入取整:(2.1)=2四舍五入取整:(2.5)=3四舍五入取整:(2.9)=3凑整:Math.ceil(2)=2凑整:Math.ceil(2.1)=3凑整:Math.ceil(2.5)=3凑整:Math.ceil(2.9)=3舍掉小数取整:Math.floor(-2)=-2舍掉小数取整:Math.floor(-2.1)=-3舍掉小数取整:Math.floor(-2.5)=-3舍掉小数取整:Math.floor(-2.9)=-3四舍五入取整:(-2)=-2四舍五入取整:(-2.1)=-2四舍五入取整:(-2.5)=-3四舍五入取整:(-2.9)=-3凑整:Math.ceil(-2)=-2凑整:Math.ceil(-2.1)=-2凑整:Math.ceil(-2.5)=-2凑整:Math.ceil(-2.9)=-2