java 取整 四舍五入

package test;

import java.math.BigDecimal;

public class RoundHalfOff {

	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));
	}
}