例子1（double型强制转换成int型）：
直接舍掉小数，只留下整数。
正数：
double d = 5.5;
int i = (int)d;
System.out.println("i=："i); //输出5
double b = 5.9;
int i1 = (int)b;
System.out.println("i1=："i1); //输出5
double c = 5.2;
int i2 = (int)c;
System.out.println("i2=："i2); //输出5
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负数：
double d = -5.5;
int i = (int)d;
System.out.println("i=："i); //输出-5
double b = -5.9;
int i1 = (int)b;
System.out.println("i1=："i1); //输出-5
double c = -5.2;
int i2 = (int)c;
System.out.println("i2=："i2); //输出-5
例子2（三种取整的方法）：
向上取整：Math.ceil(double a)
向下取整：Math.floor(double a)
四舍五入取整：Math.round(double a)
这里要注意Math.round(double a)和Math.rint(double a)，四舍五入取整要用Math.round(double a)，千万不要用Math.rint(double a)，后面我会再详细写Math.round(double a)和Math.rint(double a)的区别
double a = 35;
double b = 20;
double c = a/b; //等于1.75
System.out.println(c); //输出1.75
System.out.println(Math.ceil(c)); //向上取整输出2.0
System.out.println(Math.floor(c)); //向下取整输出1.0
System.out.println(Math.round(c)); //四舍五入取整输出2.0
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原文：https://blog.csdn.net/xmc281141947/article/details/53887126