java Math.floor，Math.ceil，Math.rint，Math.round用法詳解

Math.floor函數講解

floor原意：地板。Math.floor函數是求一個浮點數的地板，就是求一個最接近它的整數，它的值小於或等於這個浮點數。看下面的例子：

public class Test
{
    public static void main(String[] args)
    {
        System.out.println("Math.floor(-1.1): " + Math.floor(-1.1));
        System.out.println("Math.floor(-1.5): " + Math.floor(-1.5));
        System.out.println("Math.floor(-1.6): " + Math.floor(-1.6));
        System.out.println("Math.floor(0.1): " + Math.floor(0.1));
        System.out.println("Math.floor(0.5): " + Math.floor(0.5));
        System.out.println("Math.floor(0.6): " + Math.floor(0.6));
        System.out.println("Math.floor(1.1): " + Math.floor(1.1));
        System.out.println("Math.floor(1.5): " + Math.floor(1.5));
        System.out.println("Math.floor(1.6): " + Math.floor(1.6));
    }
}

結果爲：
Math.floor(-1.1): -2.0
Math.floor(-1.5): -2.0
Math.floor(-1.6): -2.0
Math.floor(0.1): 0.0
Math.floor(0.5): 0.0
Math.floor(0.6): 0.0
Math.floor(1.1): 1.0
Math.floor(1.5): 1.0
Math.floor(1.6): 1.0

Math.ceil函數講解

ceil願意：天花板。Math.ceil函數執行的是向上取整計算，它返回的是大於或等於函數參數，並且與之最接近的整數。看下面的例子：

public class Test
{
    public static void main(String[] args)
    {
        System.out.println("Math.ceil(-1.1): " + Math.ceil(-1.1));
        System.out.println("Math.ceil(-1.5): " + Math.ceil(-1.5));
        System.out.println("Math.ceil(-1.6): " + Math.ceil(-1.6));
        System.out.println("Math.ceil(0.1): " + Math.ceil(0.1));
        System.out.println("Math.ceil(0.5): " + Math.ceil(0.5));
        System.out.println("Math.ceil(0.6): " + Math.ceil(0.6));
        System.out.println("Math.ceil(1.1): " + Math.ceil(1.1));
        System.out.println("Math.ceil(1.5): " + Math.ceil(1.5));
        System.out.println("Math.ceil(1.6): " + Math.ceil(1.6));
    }
}

結果爲：
Math.ceil(-1.1): -1.0
Math.ceil(-1.5): -1.0
Math.ceil(-1.6): -1.0
Math.ceil(0.1): 1.0
Math.ceil(0.5): 1.0
Math.ceil(0.6): 1.0
Math.ceil(1.1): 2.0
Math.ceil(1.5): 2.0
Math.ceil(1.6): 2.0

Math.rint函數講解

Math.rint函數返回最接近參數的整數，如果有2個數同樣接近，則返回偶數的那個。

public class Test
{
    public static void main(String[] args)
    {
        System.out.println("Math.rint(-1.1): " + Math.rint(-1.1));
        System.out.println("Math.rint(-1.5): " + Math.rint(-1.5));
        System.out.println("Math.rint(-1.6): " + Math.rint(-1.6));
        System.out.println("Math.rint(0.1): " + Math.rint(0.1));
        System.out.println("Math.rint(0.5): " + Math.rint(0.5));
        System.out.println("Math.rint(0.6): " + Math.rint(0.6));
        System.out.println("Math.rint(1.1): " + Math.rint(1.1));
        System.out.println("Math.rint(1.5): " + Math.rint(1.5));
        System.out.println("Math.rint(1.6): " + Math.rint(1.6));
    }
}

結果爲：
Math.rint(-1.1): -1.0
Math.rint(-1.5): -2.0
Math.rint(-1.6): -2.0
Math.rint(0.1): 0.0
Math.rint(0.5): 0.0
Math.rint(0.6): 1.0
Math.rint(1.1): 1.0
Math.rint(1.5): 2.0
Math.rint(1.6): 2.0

Math.round函數講解

round方法，它表示”四捨五入”，算法爲Math.floor(x+0.5)，即將原來的數字加上0.5後再向下取整

public class Test
{
    public static void main(String[] args)
    {
        System.out.println("Math.round(-1.1): " + Math.round(-1.1));
        System.out.println("Math.round(-1.5): " + Math.round(-1.5));
        System.out.println("Math.round(-1.6): " + Math.round(-1.6));
        System.out.println("Math.round(0.1): " + Math.round(0.1));
        System.out.println("Math.round(0.5): " + Math.round(0.5));
        System.out.println("Math.round(0.6): " + Math.round(0.6));
        System.out.println("Math.round(1.1): " + Math.round(1.1));
        System.out.println("Math.round(1.5): " + Math.round(1.5));
        System.out.println("Math.round(1.6): " + Math.round(1.6));
    }
}

結果爲：
Math.round(-1.1): -1
Math.round(-1.5): -1
Math.round(-1.6): -2
Math.round(0.1): 0
Math.round(0.5): 1
Math.round(0.6): 1
Math.round(1.1): 1
Math.round(1.5): 2
Math.round(1.6): 2

轉載自：Math.floor，Math.ceil，Math.rint，Math.round用法詳解