Java Tutorial/Class Definition/Varargs

Demonstrate variable-length arguments.

class VarArgs {
  // vaTest() now uses a vararg.
  static void vaTest(int... v) {
    System.out.print("Number of args: " + v.length + " Contents: ");
    for (int x : v)
      System.out.print(x + " ");
    System.out.println();
  }
  public static void main(String args[]) {
    vaTest(10); // 1 arg
    vaTest(1, 2, 3); // 3 args
    vaTest(); // no args
  }
}

Demonstrating variable-length arguments

A variable-length argument is specified by three periods (...).

static void yourMethodInVarargs(int ... v) {}

Number of args: 1 Contents: 10 
Number of args: 3 Contents: 1 2 3 
Number of args: 0 Contents:

Limiting the object Types in a Variable Argument List

public class MainClass {
  public static void main(String[] args) {
    System.out.println(average(1.0, 2.0, 3.0, 4.0, 5.0));
    System.out.println(average(3.14, 1.414, 1.732));
    System.out.println(average(new Double(7), new Double(8), new Double(9), new Double(10)));
  }
  // Average of a variable number of values
  public static double average(Double... args) {
    if (args.length == 0) {
      return 0.0;
    }
    double ave = 0.0;
    for (double value : args) {
      ave += value;
    }
    return ave / args.length;
  }
}

3.0
2.0953333333333335
8.5

Make methods that have unspecified number of parameters:pass an array of Objects

public class Main {
  public static void main(String args[]) {
    myMethod(new Object[] { "value 1", new Integer(2), "value n" });
  }
  public static void myMethod(Object parms[]) {
    for (int i = 0; i < parms.length; i++)
      System.out.println(parms[i]);
  }
}

Methods Accepting a Variable Number of objects

public class MainClass {
  public static void main(String[] args) {
    printAll(2, "two", 4, "four", 4.5, "four point five"); 
    printAll();
    printAll(25, "Anything goes", true, 4E4, false);
  }
  public static void printAll(Object... args) {
    for (Object arg : args) {
      System.out.print("  " + arg);
    }
    System.out.println();
  }
}

2  two  4  four  4.5  four point five
25  Anything goes  true  40000.0  false

Overloading Vararg Methods

class MainClass {
  static void vaTest(int... v) {
    System.out.print("vaTest(int ...): " + "Number of args: " + v.length + " Contents: ");
    for (int x : v)
      System.out.print(x + " ");
    System.out.println();
  }
  static void vaTest(boolean... v) {
    System.out.print("vaTest(boolean ...) " + "Number of args: " + v.length + " Contents: ");
    for (boolean x : v)
      System.out.print(x + " ");
    System.out.println();
  }
  static void vaTest(String msg, int... v) {
    System.out.print("vaTest(String, int ...): " + msg + v.length + " Contents: ");
    for (int x : v)
      System.out.print(x + " ");
    System.out.println();
  }
  public static void main(String args[]) {
    vaTest(1, 2, 3);
    vaTest("Testing: ", 10, 20);
    vaTest(true, false, false);
  }
}

Use varargs with standard arguments.

public class MainClass {
  static void vaTest(String msg, int... v) {
    System.out.print(msg + v.length + " Contents: ");
    for (int x : v)
      System.out.print(x + " ");
    System.out.println();
  }
  public static void main(String args[]) {
    vaTest("One vararg: ", 10);
    vaTest("Three varargs: ", 1, 2, 3);
    vaTest("No varargs: ");
  }
}

Using varargs with standard arguments

A method can have "normal" parameters along with a variable-length parameter. However, the variable-length parameter must be the last parameter.

There must be only one varargs parameter.

int aMethod(int a, int b, double c, int ... vals) {}

One vararg: 1 Contents: 10 
Three varargs: 3 Contents: 1 2 3 
No varargs: 0 Contents: