//三種方法
//負(fù)數(shù)和正數(shù)的整數(shù)情況需要分開(kāi)考慮
import java.util.*;
public class Split {
	
	public static void main(String[] args) {
		float num,b;
		int a,pointIndex;
		
		Scanner s = new Scanner(System.in);
		System.out.println("請(qǐng)輸入一個(gè)float數(shù)：");
		num = s.nextFloat();
//		判斷正負(fù)
		if(num >=0) {
//			正數(shù)部分計(jì)算
//			方法一：直接轉(zhuǎn)換數(shù)字類型后加減，問(wèn)題是轉(zhuǎn)換類型會(huì)導(dǎo)致小數(shù)部分變化，不知道怎么解決??！
			a = (int) num;
			b = num - a;
			System.out.println(num + "整數(shù)部分：" + a);
			System.out.println(num + "小數(shù)部分：" + b);
			
//			方法二：轉(zhuǎn)換成字符串，用方法split按小數(shù)點(diǎn)前后分割
			String str = String.valueOf(num);                   //將float類型轉(zhuǎn)換成字符串
			String[] ary = str.split("\\.");			
			System.out.println(num + "整數(shù)部分為：" + ary[0]);
			System.out.println(num + "小數(shù)部分為：" + "0." + ary[1]);
			
//			方法三：同樣轉(zhuǎn)換成字符串，用方法indexOf標(biāo)記小數(shù)點(diǎn)位置
			pointIndex = str.indexOf('.');
			System.out.println(num + "的整數(shù)部分為：" + str.substring(0,pointIndex));
			System.out.println(num + "的小數(shù)部分為：" + "0" + str.substring(pointIndex,str.length()));			
	    }
		
//		負(fù)數(shù)部分計(jì)算，注意，-1.7的正數(shù)部分是-2，小數(shù)部分是0.3
		else {
//			方一
			a = (int) num - 1;
			b = num - a;
			System.out.println(num + "整數(shù)部分：" + a);
			System.out.println(num + "小數(shù)部分：" + b);
//			方二
			String str = String.valueOf(num);                   //將float類型轉(zhuǎn)換成字符串
			String[] ary = str.split("\\.");	
			a = Integer.parseInt(ary[0]) -1;
			b = 1 - Float.parseFloat("0." + ary[1]);            //需要計(jì)算，再次轉(zhuǎn)換成float類型
			System.out.println(num + "整數(shù)部分為：" + a);
			System.out.println(num + "小數(shù)部分為：" + b);
			
//			方三
			pointIndex = str.indexOf('.');
			a = Integer.parseInt(str.substring(0,pointIndex)) -1;
			b = 1 - Float.parseFloat("0" + str.substring(pointIndex));
			System.out.println(num + "的整數(shù)部分為：" + a);
			System.out.println(num + "的小數(shù)部分為：" + b);						
		}				
	}
}

Math.ceil() //只要有小數(shù)都+1

Math.floor() //不取小數(shù)

Math.round() //四舍五入