Runtime vs Compile Time

[deep dove]

@obsidian orchid has a question:

charlie222223

what the different betweeen runtime and compile time, i am quite confusing

<@&987246399047479336> please have a look, thanks.

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TJ-Bot

What the different betweeen runtime and compile time, i am quite confusing

Compile time refers to the period during which the code is being translated into machine code by the compiler. Any syntax errors or logic errors in the code are detected during compile time, and the code must be corrected before it can be successfully compiled.

Runtime, on the other hand, refers to the period during which the program is actually running and executing its instructions. During runtime, input data is processed and output is generated based on the instructions provided in the code. Errors that occur during runtime are known as runtime errors, and they can cause a program to crash or behave unexpectedly.

In summary, compile time is when the code is being compiled into machine code, and any errors must be fixed before compilation can be successful. Runtime is when the program is actually running and executing its instructions, and errors that occur during this time are known as runtime errors. Understanding these distinctions can help developers troubleshoot issues more effectively in their Java programs.

- AI generated response

[velvet flax]

in java, ur code goes through several stages

1. u write the source code and put it into a file. for example Foo.java

2. u run the command javac Foo.java, this will compile the source code to bytecode

the result of step 2 is a new file called Foo.class

3. u execute the bytecode by running the command java Foo

this will run the Foo.class file

any error that happens at step 2 is called compile time error

any error that happens at step 3 is called runtime error

if u think about a project like, lets say minecraft, compile time errors happen on the developers machine. the people who make minecraft

while runtime errors happen on the user side. the people who play minecraft

[obsidian orchid]

thanks , i need this

[velvet flax]

👍

the main reason why this split exists and why u dont just send the source files to the users and they run it "directly" is mostly bc of performance

the compiled bytecode has been translated in a way that makes it faster and easier to understand for the machine than the source code

so running the bytecode is easier/faster than if u would have to go of the source code directly

but there are languages that drop this extra step and dont care for the performance loss

like python. we call these languages interpreted languages

since they will interpret the source code directly when running

instead of having a separate compilation step beforehand

java is somewhat in the middle, having its virtual machine the JVM. i.e. the bytecode (Foo.class) isnt yet the "final final" code that ur CPU can run yet either. there is another step in between where the JVM will take the bytecode and translate it to true "machine code" which is then executed

languages like C/C++ dont have this and when u compile their source code the output is directly the "final final machine code", Foo.exe

the disadvantage of that is that its not platform independent anymore. this executable only runs on this type of machine, not on for example a mac anymore

this is called ahead-of-time compilation

(versus just-in-time compilation)

[hazy grove]

when the JVM does just in time compilation with the bytecode, it will also try to optimize the compiled machine code
e.g. when an if statement is always false, it will just strip this if from the machine code 😄

so a Java app can get more performant the longer it runs, if it does always the same