Java取整数

String arch = System.getProperty("sun.arch.data.model");

舍掉小数取整:Math.floor(2.0)=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
舍掉小数取整:Math.floor(-2.0)=-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:Math.rint(2.0)=2
四舍五入取整:Math.rint(2.1)=2
四舍五入取整:Math.rint(2.5)=2
四舍五入取整:Math.rint(2.9)=3
四舍五入取整:Math.rint(-2.0)=-2
四舍五入取整:Math.rint(-2.1)=-2
四舍五入取整:Math.rint(-2.5)=-2
四舍五入取整:Math.rint(-2.9)=-3

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(" + i + ")=" + (int) Math.floor(i)); 
System.out.println("舍掉小数取整:Math.floor(" + j + ")=" + (int) Math.floor(j)); 
System.out.println("舍掉小数取整:Math.floor(" + k + ")=" + (int) Math.floor(k)); 
System.out.println("舍掉小数取整:Math.floor(" + m + ")=" + (int) Math.floor(m)); 
System.out.println(); 

System.out.println("舍掉小数取整:Math.floor(-" + i + ")=" + (int) Math.floor(-i)); 
System.out.println("舍掉小数取整:Math.floor(-" + j + ")=" + (int) Math.floor(-j)); 
System.out.println("舍掉小数取整:Math.floor(-" + k + ")=" + (int) Math.floor(-k)); 
System.out.println("舍掉小数取整:Math.floor(-" + m + ")=" + (int) Math.floor(-m)); 
System.out.println(); 

// 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(" + i + ")=" + (int) Math.rint(i)); 
System.out.println("四舍五入取整:Math.rint(" + j + ")=" + (int) Math.rint(j)); 
System.out.println("四舍五入取整:Math.rint(" + k + ")=" + (int) Math.rint(k)); 
System.out.println("四舍五入取整:Math.rint(" + m + ")=" + (int) Math.rint(m)); 
System.out.println(); 

System.out.println("四舍五入取整:Math.rint(-" + i + ")=" + (int) Math.rint(-i)); 
System.out.println("四舍五入取整:Math.rint(-" + j + ")=" + (int) Math.rint(-j)); 
System.out.println("四舍五入取整:Math.rint(-" + k + ")=" + (int) Math.rint(-k)); 
System.out.println("四舍五入取整:Math.rint(-" + m + ")=" + (int) Math.rint(-m)); 
System.out.println(); 

System.out.println("DecimalFormat四舍五入取整:(" + i + ")=" 
+ new DecimalFormat("0").format(i)); 
System.out.println("DecimalFormat四舍五入取整:(" + j + ")=" 
+ new DecimalFormat("0").format(j)); 
System.out.println("DecimalFormat四舍五入取整:(" + k + ")=" 
+ new DecimalFormat("0").format(k)); 
System.out.println("DecimalFormat四舍五入取整:(" + m + ")=" 
+ new DecimalFormat("0").format(m)); 
System.out.println(); 

System.out.println("DecimalFormat四舍五入取整:(-" + i + ")=" 
+ new DecimalFormat("0").format(-i)); 
System.out.println("DecimalFormat四舍五入取整:(-" + j + ")=" 
+ new DecimalFormat("0").format(-j)); 
System.out.println("DecimalFormat四舍五入取整:(-" + k + ")=" 
+ new DecimalFormat("0").format(-k)); 
System.out.println("DecimalFormat四舍五入取整:(-" + m + ")=" 
+ new DecimalFormat("0").format(-m)); 
System.out.println(); 

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

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

System.out.println("凑整:Math.ceil(" + i + ")=" + (int) Math.ceil(i)); 
System.out.println("凑整:Math.ceil(" + j + ")=" + (int) Math.ceil(j)); 
System.out.println("凑整:Math.ceil(" + k + ")=" + (int) Math.ceil(k)); 
System.out.println("凑整:Math.ceil(" + m + ")=" + (int) Math.ceil(m)); 
System.out.println(); 

System.out.println("凑整:Math.ceil(-" + i + ")=" + (int) Math.ceil(-i)); 
System.out.println("凑整:Math.ceil(-" + j + ")=" + (int) Math.ceil(-j)); 
System.out.println("凑整:Math.ceil(-" + k + ")=" + (int) Math.ceil(-k)); 
System.out.println("凑整:Math.ceil(-" + m + ")=" + (int) Math.ceil(-m)); 
System.out.println(); 

System.out.println("四舍五入取整:Math.round(" + i + ")=" + (int) Math.round(i)); 
System.out.println("四舍五入取整:Math.round(" + j + ")=" + (int) Math.round(j)); 
System.out.println("四舍五入取整:Math.round(" + k + ")=" + (int) Math.round(k)); 
System.out.println("四舍五入取整:Math.round(" + m + ")=" + (int) Math.round(m)); 
System.out.println(); 

System.out.println("四舍五入取整:Math.round(-" + i + ")=" + (int) Math.round(-i)); 
System.out.println("四舍五入取整:Math.round(-" + j + ")=" + (int) Math.round(-j)); 
System.out.println("四舍五入取整:Math.round(-" + k + ")=" + (int) Math.round(-k)); 
System.out.println("四舍五入取整:Math.round(-" + m + ")=" + (int) Math.round(-m)); 
} 

}