Use of JShell script tool in java

JShell script tool is a new feature of JDK9

When will we use JShell tool? When we write very little code and are unwilling to write Class and main method are not willing to compile and run. At this time, you can use the JShell tool.

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Start the JShell tool and enter the JShell command directly on the DOS command line.

Next, you can write Java code. There is no need to write classes and methods. You can directly write the code in the method. At the same time, there is no need to compile and run, just press Enter

Note: The JShell tool is only suitable for testing fragmented code. To develop more content, it is recommended to write it in the method.

=Expansion of symbols

Is there something wrong with the following program?

Analysis: s = 1 is logically regarded as s = s 1. The calculation result is promoted to the int type, and an error occurs when assigning a value to the short type because the result cannot be A type with a large value range is assigned to a type with a small value range. However, s=s 1 performs two operations, and = is an operator that only operates once and has the characteristics of forced conversion. That is to say, s = 1 is s = (short)(s 1), so there is no problem with the program. The compilation is passed, and the running result is 2.

Operation of constants and variables

Is there any problem with the following program?

Analysis: b3 = 1 2, 1 and 2 are constants, which are fixed data. During compilation (compiler javac), 1 2 has been determined The result does not exceed the value range of the byte type and can be assigned to variable b3, so b3=1 2 is correct.

On the contrary, b4 = b2 b3, b2 and b3 are variables, and the values ​​of the variables may change. During compilation, the compiler javac is not sure what the result of b2 b3 is, so it will convert the result as int The type is processed, so the int type cannot be assigned to the byte type, so the compilation fails.

Reflected in jshell:

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