java - Runnable with a parameter?

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Top 5 Answer for java - Runnable with a parameter?

vote vote

99

Well it's been almost 9 years since I originally posted this and to be honest, Java has made a couple improvements since then. I'll leave my original answer below, but there's no need for people to do what is in it. 9 years ago, during code review I would have questioned why they did it and maybe approved it, maybe not. With modern lambdas available, it's irresponsible to have such a highly voted answer recommending an antiquated approach (that, in all fairness, was dubious to begin with...) In modern Java, that code review would be immediately rejected, and this would be suggested:

void foo(final String str) {     Thread t = new Thread(() -> someFunc(str));     t.start(); } 

As before, details like handling that thread in a meaningful way is left as an exercise to the reader. But to put it bluntly, if you're afraid of using lambdas, you should be even more afraid of multi-threaded systems.

Original answer, just because:

You can declare a class right in the method

void Foo(String str) {     class OneShotTask implements Runnable {         String str;         OneShotTask(String s) { str = s; }         public void run() {             someFunc(str);         }     }     Thread t = new Thread(new OneShotTask(str));     t.start(); } 
vote vote

89

You could put it in a function.

String paramStr = "a parameter"; Runnable myRunnable = createRunnable(paramStr);  private Runnable createRunnable(final String paramStr){      Runnable aRunnable = new Runnable(){         public void run(){             someFunc(paramStr);         }     };      return aRunnable;  } 

(When I used this, my parameter was an integer ID, which I used to make a hashmap of ID --> myRunnables. That way, I can use the hashmap to post/remove different myRunnable objects in a handler.)

vote vote

77

theView.post(new Runnable() {     String str;     @Override                                 public void run() {         par.Log(str);                                   }     public Runnable init(String pstr) {         this.str=pstr;         return(this);     } }.init(str)); 

Create init function that returns object itself and initialize parameters with it.

vote vote

69

Since Java 8, the best answer is to use Consumer<T>:

https://docs.oracle.com/javase/8/docs/api/java/util/function/Consumer.html

It's one of the functional interfaces, which means you can call it as a lambda expression:

void doSomething(Consumer<String> something) {     something.accept("hello!"); }  ...  doSomething( (something) -> System.out.println(something) )  ... 
vote vote

56

I use the following class which implements the Runnable interface. With this class you can easily create new threads with arguments

public abstract class RunnableArg implements Runnable {      Object[] m_args;      public RunnableArg() {     }      public void run(Object... args) {         setArgs(args);         run();     }      public void setArgs(Object... args) {         m_args = args;     }      public int getArgCount() {         return m_args == null ? 0 : m_args.length;     }      public Object[] getArgs() {         return m_args;     } } 

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