JAVA取整和JAVA四舍五入方法

 

import java.math.BigDecimal;
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));
    }
}