The problem of hands-on brain and the experimental problems after class

Results:

Experimental conclusion: Enum type is a reference type!
An enumeration is not part of the original data type, and each of its specific values refers to a specific object. The same value refers to the same object.
You can use the "= =" and the Equals () methods to directly compare the values of the enumeration variables, in other words, the result of the "= =" and the Equals () methods are equivalent for variables of enum types.

2. After-school contact

Read the corresponding textbook, or use the Internet search engine, find out the anti-code, complement and the original code of the concepts, and then write a sample program, the positive numbers, negative numbers of various bit operations, observe the output, and the results of the manual calculation, to see the number in Java is the above-mentioned code representation.

The original code: is the binary fixed-point notation, that is, the highest bit is the sign bit, "0" is positive, "1" is negative, the remaining bits represent the size of the value.

Anti-code: Anti-code notation: the inverse code of a positive number is the same as its original code; the inverse of a negative number is a bitwise negation of its original code, except for the sign bit.

Complement: The complement notation stipulates that the complement of a positive number is the same as its original code; the complement of a negative number is added to the minus 1 of its inverse code.

3. Hands-on brain

Why is the numeric value of a double type not "mathematically accurate" result?

This involves the conversion of binary and decimal. N-binary can be understood as: the power of the numerical x cardinality, for example, we are familiar with the decimal number 123.4=1x10²+2x10+3x (10 of the 0 power) +4x (10-1 power); the other binary is the same, such as the binary number 11.01=1x2+1x (2 Power 0) +0+ 1x (2 to 2 power) = 3.25 decimal. A value of type double takes 64bit, or 64 binary numbers, except that the highest bit represents the positive and negative sign, and the lowest bit is bound to have an error with the actual data (unless the actual data is exactly 2 of the n-th square). For example, for example, to use 4bit to represent decimal 3.26, from high to low to correspond to 2 1,0,-1,-2 power, according to the top of the analysis, should be in the binary number 11.01 (corresponding to the decimal 3.25) and 11.10 (corresponding to the decimal 3.5) between the selection. in short, we give the value, in most cases need more than 64bit more digits to accurately represent (even need infinity), and the double type of the value of only 64bit, the number of bits behind will definitely bring error, can not get "mathematically accurate" The result.

4. Hands-on brain

What is the output of the following code?

Why is there such an output result?

The first sentence outputs the "+" connection literal, and the result is that x and Y will connect the two data.

The "+" in the two outputs of the statement is the operator, and the result is the sum of x and Y.

The problem of hands-on brain and the experimental problems after class