Arithmetic rule between the basic data types: cast automatic conversion

1. Automatic lifting type
herein discussed only seven kinds of operation data (does not include Boolean, Boolean because only two situations: false and true)

When a small capacity data type variable capacity type of data variables do arithmetic, the result is automatically promoted to a large capacity of data types
i.e., small capacity data type variable + capacity data type variable = large-capacity data type variable
byte → short → int → long → float → double

Note: in this case refers to the capacity size represents a range of large and small numbers.
For example: float capacity greater than the capacity of the long

In particular: when the byte, short, char three types of variables do calculation result to an int

class Test{
	public static void main(String[] args) {
		
		byte b1 = 2;
		int i1 = 129;
		//编译不通过
		//byte b2 = b1 + i1;
		int i2 = b1 + i1;
		long l1 = b1 + i1;
		System.out.println(i2);

		float f = b1 + i1;
		System.out.println(f);

		short s1 = 123;
		double d1 = s1;
		System.out.println(d1);//123.0

		//***************特别地*********************
		char c1 = 'a';//97
		int i3 = 10;
		int i4 = c1 + i3;
		System.out.println(i4);

		short s2 = 10;
		//char c2  = c1 + s2;//编译不通过

		byte b2 = 10;
		//char c3 = c1 + b2;//编译不通过
		//short s3 = b2 + s2;//编译不通过
		//short s4 = b1 + b2;//编译不通过
	}
}

2. cast: automatic type lifting operation of an inverse operation
① to use strong turn symbol ()
② note, cast, may result in loss of precision
small-capacity variable type data → data type variable capacity, without losing original information.
The data type of the variable capacity → small-capacity data type variable, you may lose the original message.

class Test1 {
	public static void main(String[] args) {
		double d1 = 12.9;
		//精度损失举例1
		int i1 = (int)d1;//截断操作
		System.out.println(i1);

		//没有精度损失
		long l1 = 123;
		short s2 = (short)l1;
		
		//精度损失举例2
		int i2 = 128;
		byte b = (byte)i2;
		System.out.println(b);//-128
	}
}