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Is Java pass by reference?

when I used some java class like (Integer, File, Boolean) if I pass the instance as an argument to a function and try to change its value after I use this value outside function, the value remains unchanged.

例如:

private void run(){
        File tmpFile;
        setFile(tmpFile);
        System.out.println(tmpFile.getAbsolutePath());  //error tmpFile is null
    }

private void setFile(File xFile){
    xFile = jFileChooser.getSelectedFile();  // this returned object file
}

Answer 1

The short answer is that Java uses call-by-value, not call-by-reference.

在您的<代码>File方法中,您被指派到x。文件只改动了当地变量。它不改动<代码>tmpFile在<代码>run(方法中的位置。

您应撰写该守则,以便setFile回归数值;例如:

    private void run(){
        File tmpFile = getFile();
        System.out.println(tmpFile.getAbsolutePath());
    }

    private File getFile() {
        return jFileChooser.getSelectedFile();
    }

(说明:我改变了方法名称,因为一种名为<代码>的方法。) iii 确实没有做任何事情,令人极为怀疑。

Answer 2

Java always passes by value. You shouldn t expect any other behaviour.

A method can only change an object when you pass a reference (The reference is still passed by value)

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