java取整和java四舍五入方法

import java.math.BigDecimal;
import java.text.DecimalFormat;
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));
System.out.println("舍掉小数取整:Math.floor(2.1)=" + (int)Math.floor(j));
System.out.println("舍掉小数取整:Math.floor(2.5)=" + (int)Math.floor(k));
System.out.println("舍掉小数取整:Math.floor(2.9)=" + (int)Math.floor(m));

/* 这段被注释的代码不能正确的实现四舍五入取整
System.out.println("四舍五入取整:Math.rint(2)=" + (int)Math.rint(i));
System.out.println("四舍五入取整:Math.rint(2.1)=" + (int)Math.rint(j));
System.out.println("四舍五入取整:Math.rint(2.5)=" + (int)Math.rint(k));
System.out.println("四舍五入取整:Math.rint(2.9)=" + (int)Math.rint(m));

System.out.println("四舍五入取整:(2)=" + new DecimalFormat("0").format(i));
System.out.println("四舍五入取整:(2.1)=" + new DecimalFormat("0").format(i));
System.out.println("四舍五入取整:(2.5)=" + new DecimalFormat("0").format(i));
System.out.println("四舍五入取整:(2.9)=" + new DecimalFormat("0").format(i));
*/

System.out.println("四舍五入取整:(2)=" + new BigDecimal("2").setScale(0, BigDecimal.ROUND_HALF_UP));
System.out.println("四舍五入取整:(2.1)=" + new BigDecimal("2.1").setScale(0, BigDecimal.ROUND_HALF_UP));
System.out.println("四舍五入取整:(2.5)=" + new BigDecimal("2.5").setScale(0, BigDecimal.ROUND_HALF_UP));
System.out.println("四舍五入取整:(2.9)=" + new BigDecimal("2.9").setScale(0, BigDecimal.ROUND_HALF_UP));
System.out.println("凑整:Math.ceil(2)=" + (int)Math.ceil(i));
System.out.println("凑整:Math.ceil(2.1)=" + (int)Math.ceil(j));
System.out.println("凑整:Math.ceil(2.5)=" + (int)Math.ceil(k));
System.out.println("凑整:Math.ceil(2.9)=" + (int)Math.ceil(m));
System.out.println("舍掉小数取整:Math.floor(-2)=" + (int)Math.floor(-i));
System.out.println("舍掉小数取整:Math.floor(-2.1)=" + (int)Math.floor(-j));
System.out.println("舍掉小数取整:Math.floor(-2.5)=" + (int)Math.floor(-k));
System.out.println("舍掉小数取整:Math.floor(-2.9)=" + (int)Math.floor(-m));

System.out.println("四舍五入取整:(-2)=" + new BigDecimal("-2").setScale(0, BigDecimal.ROUND_HALF_UP));
System.out.println("四舍五入取整:(-2.1)=" + new BigDecimal("-2.1").setScale(0, BigDecimal.ROUND_HALF_UP));
System.out.println("四舍五入取整:(-2.5)=" + new BigDecimal("-2.5").setScale(0, BigDecimal.ROUND_HALF_UP));
System.out.println("四舍五入取整:(-2.9)=" + new BigDecimal("-2.9").setScale(0, BigDecimal.ROUND_HALF_UP));
System.out.println("凑整:Math.ceil(-2)=" + (int)Math.ceil(-i));
System.out.println("凑整:Math.ceil(-2.1)=" + (int)Math.ceil(-j));
System.out.println("凑整:Math.ceil(-2.5)=" + (int)Math.ceil(-k));
System.out.println("凑整:Math.ceil(-2.9)=" + (int)Math.ceil(-m));
}
}

/* Output:
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
*///:~