表达式的类型转换

一段小程序来解释表达式中的各个数据类型的转换机制。

package com.liaojianya.chapter1;
/**
 * This program demonstrates the convertion of data type.
 * @author LIAO JIANYA
 *
 */
public class TypeConvert6_17
{
	public static void main(String[] args)
	{
		char ch = 'a';
		short a = -2;
		int b = 3;
		float f = 5.3f;
		double d = 6.28;

		System.out.println("ch / a = " + ch / a);
		System.out.println("the type of (ch / a) is :  " + getType((ch / a)));
		
		System.out.println("d / f = " + d / f);
		System.out.println("the type of (d / f) is :  " + getType((d / f)));
		
		System.out.println("a + b = " + (a + b));
		System.out.println("the type of (a + b) is :  " + getType((a + b)));
		
		System.out.println("(ch / a) - (d / f) - (a + b) = " + ((ch / a) - (d / f) - (a + b)));		
		System.out.println("the type of ((ch / a) - (d / f) - (a + b)) is :  " 
		+ getType(((ch / a) - (d / f) - (a + b))));
	}
		public static String getType(Object o)
		{
			return o.getClass().toString();
		}
		public static String getType(int o)
		{
			return "int";
		}
		public static String getType(char o)
		{
			return "char";
		}
		public static String getType(short o)
		{
			return "short";
		}
		public static String getType(float o)
		{
			return "short";
		}
		public static String getType(double o)
		{
			return "double";
		}

}

　　运行结果：

ch / a = -48
the type of (ch / a) is :  int
d / f = 1.1849056177353188
the type of (d / f) is :  double
a + b = 1
the type of (a + b) is :  int
(ch / a) - (d / f) - (a + b) = -50.18490561773532
the type of ((ch / a) - (d / f) - (a + b)) is :  double

　分析：

　1）占用字节较少的数据类型转换成占用字节较多的数据类型。

　2）字符类型会转换成int类型。

　3）int类型会转换成float类型。

　4）表达式中出现double，则其他操作数也会转换成double类型。

　5）总结：大鱼吃小鱼：占字节多的替换占字节少的；精度高的优先；优先级排序：byte，short，int，long，float，double。