How to enable Intellij hot code swap

Question

Intellij does not seem to be doing basic hot code swap on my installation.

For this code:

public class MainTest {
    public void method1() {
        System.out.println("Breakpoint here");
    }

    public void method2() {
        System.out.println("Line that will get 24 modified");
    }

    public static void main(String[] args) {
        System.out.println("First print here");
        MainTest mainTest = new MainTest();
        mainTest.method1();
        mainTest.method2();
        System.out.println("Line that I do not modify");
    }
}

I put a breakpoint on mainTest.method1(); then modify the string at method2(), hit ctrl+s and continue to step by step. Unfortunately the runtime is not updated, old string is being printed. Full stop - compile - run does print the new string. So my conclusion is hot-swap not working.

Is there any settings I need to set to enable hot code swap?

• Ubuntu, JDK 1.6
• Intellij 10.5 Ultimate (evaluation)

Answer 1

I wanted hotswap to automatically run every time I saved a Java file. None of the other answers did this so I just:

1. Created a macro that will run on save: https://stackoverflow.com/a/5581992/14731
2. Added Action: Hotswap at the end of the macro (Run -> Reload Changed Classes)

Answer 2

There is a Debugger > HotSwap option in intellij 11.

Answer 3

Go to Setting --> Select Debug --> HotSwap

Answer 4

I encountered this problem on Ubuntu. I also had an apparently unrelated issue where IntelliJ gave an error about the file watch limit (my apologies that I no longer have the exact error message). To solve this later issue I did the following steps:

1. Add the following line to either /etc/sysctl.conf file or a new *.conf file (e.g. idea.conf) under /etc/sysctl.d/ directory:

   fs.inotify.max_user_watches = 524288
   

2. Then run this command to apply the change:

   sudo sysctl -p --system

Now my React components rebuild and hot swap just fine.

Source

Answer 5

After below modifications and enabling hot swap, a change in a Java file took 1-2 seconds of restart time. (Initial start time is around 7 seconds for me).

I hope below method helps...

---

First, you need to check “Make project automatically” in preferences menu.

To open preferences menu;

you can go to top menu and click;

IntelliJ IDEA -> Preferences

or you can type below shortcut via keyboard;

cmd + option + s

Then, you can check Make project automatically as in below picture;

Secondly, you need to modify compiler.automake.allow.when.app.running registry setting as true.

To open registry, you need to click below keyboard shortcut:

cmd + shift + a

Type registry as in below picture, select Registry, and hit enter button of keyboard;

After Registry window opened, type compiler.automake to see compiler.automake.allow.when.app.running option, and check it as in below picture;

Than, you need to restart IntelliJ to make registry changes work.

Answer 6

After saving your class while waiting on your breakpoint just recompile your class with Build -> Compile 'MainTest.java' or press Ctrl+Shift+F9 with the standard key bindings.

IntelliJ IDEA will then show a small dialog in which it asks you if you want to reload that class.