如何在构造中设置默认参数值？

Question

Can I set the default arument value in Construct function something like ?

public class XLSReader {
  public XLSReader(String filename="XYZ.xls") {
  }
}

Answer 1

No. Java doesn't support optional parameters. You can use overloading and chaining though:

public XlsReader() {
    this("XYZ.xls");
}

public XlsReader(String filename) {
    // Use filename here
}

(This applies to methods as well as constructors.)

Answer 2

No, you can't. Default parameter is not supported in Java.

Answer 3

No you cannot but what you can do is to have 2 constructors like this:

public class XLSReader {
  String filename;

  // constructor with a filename argument
  public XLSReader(String filename) {
     this.filename = filename;
  }

  // default constructor will fill-in "default value" XYZ.xls
  public XLSReader() {
     this.filename = "XYZ.xls";
  }
}