4 ms·

I like the clever use of the "java prog.java" style. I don't know how many folks know, although its been there for a bit, that you no longer have to specifical

I like the clever use of the "java prog.java" style. I don't know how many folks know, although its been there for a bit, that you no longer have to specifically compile single file java programs. You can just run them with with "java prog.java". (Honestly, I haven't used the technique myself, still old school -- even with silly small x.java tests and such. Muscle memory and all that.)

grishka 2y ago
I do it a lot. These single-file programs can be called Java scripts when run without compilation.
- apantel 2y ago
  I wonder what could be done with Java script…
  - bionsystem 2y ago
    Sounds like a name that could have some success. Given that the logo for Java is a cup of coffee, maybe we could also call it "Coffee script".
- mbreese 2y ago
  Can you add a shebang line and have it truly be a script? I do self executing JARs with a bash stub/header all the time, but haven’t tried with this.
  - grishka 2y ago
    Sadly you can't, Java doesn't support comments starting with # $ ./shebang.java ./shebang.java:1: error: illegal character: '#' #!/usr/bin/java ^ ./shebang.java:1: error: class, interface, enum, or record expected #!/usr/bin/java ^ 2 errors error: compilation failed Self-executable jars though, that's an interesting idea. No reason why it can't work, zip archives are read from the end, you can put anything in the beginning, including "#!/usr/bin/java -jar"
    - spullara 2y ago
      this has worked since the beginning but i don't think many people know about it
    - jnellis 2y ago
      I believe you can use shebang since java 11 but you can't have the filename extension be .java.
      - grishka 2y ago
        It turns out you indeed can: https://news.ycombinator.com/item?id=40912444 https://news.ycombinator.com/item?id=40912444
    - mbreese 2y ago
      For the self executing JAR, I normally add a bash/shell stub for the header that ends with java -jar $0 The rest of it sets up the environment (JAVA_OPTS, -Xmx, etc).
- metadat 2y ago
  How do you run a Java program without compilation?
  - grishka 2y ago
    It technically compiles it to memory before running it, but the point is that you don't have to invoke javac first. It's a relatively new feature.
    - metadat 2y ago
      Do you know for which Java version this first became available?
      - grishka 2y ago
        11: https://openjdk.org/jeps/330 https://openjdk.org/jeps/330 Oh so actually, you can use a shebang, just without the .java extension and with the "--source" flag, it's specifically written out in that spec. I was doing my experiment wrong!
        metadat 2y ago
        Awesome, thanks for sharing!
- tpoacher 2y ago
  though, in theory java has jshell for java-based shell scripts specifically
oftenwrong 2y ago
You can run multi-file source-code programs as of JDK 22: https://openjdk.org/jeps/458 https://openjdk.org/jeps/458

grishka 2y ago

I do it a lot. These single-file programs can be called Java scripts when run without compilation.

apantel 2y ago
I wonder what could be done with Java script…
- bionsystem 2y ago
  Sounds like a name that could have some success. Given that the logo for Java is a cup of coffee, maybe we could also call it "Coffee script".
mbreese 2y ago
Can you add a shebang line and have it truly be a script? I do self executing JARs with a bash stub/header all the time, but haven’t tried with this.
- grishka 2y ago
  Sadly you can't, Java doesn't support comments starting with # $ ./shebang.java ./shebang.java:1: error: illegal character: '#' #!/usr/bin/java ^ ./shebang.java:1: error: class, interface, enum, or record expected #!/usr/bin/java ^ 2 errors error: compilation failed Self-executable jars though, that's an interesting idea. No reason why it can't work, zip archives are read from the end, you can put anything in the beginning, including "#!/usr/bin/java -jar"
  - spullara 2y ago
    this has worked since the beginning but i don't think many people know about it
  - jnellis 2y ago
    I believe you can use shebang since java 11 but you can't have the filename extension be .java.
    - grishka 2y ago
      It turns out you indeed can: https://news.ycombinator.com/item?id=40912444 https://news.ycombinator.com/item?id=40912444
  - mbreese 2y ago
    For the self executing JAR, I normally add a bash/shell stub for the header that ends with java -jar $0 The rest of it sets up the environment (JAVA_OPTS, -Xmx, etc).
metadat 2y ago
How do you run a Java program without compilation?
- grishka 2y ago
  It technically compiles it to memory before running it, but the point is that you don't have to invoke javac first. It's a relatively new feature.
  - metadat 2y ago
    Do you know for which Java version this first became available?
    - grishka 2y ago
      11: https://openjdk.org/jeps/330 https://openjdk.org/jeps/330 Oh so actually, you can use a shebang, just without the .java extension and with the "--source" flag, it's specifically written out in that spec. I was doing my experiment wrong!
      - metadat 2y ago
        Awesome, thanks for sharing!
tpoacher 2y ago
though, in theory java has jshell for java-based shell scripts specifically

oftenwrong 2y ago

You can run multi-file source-code programs as of JDK 22: https://openjdk.org/jeps/458 https://openjdk.org/jeps/458