Java Tutorial/Class Definition/Varargs

Demonstrate variable-length arguments.

   <source lang="java">

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
 }

}</source>

Demonstrating variable-length arguments

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

   <source lang="java">

static void yourMethodInVarargs(int ... v) {}</source>

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

   <source lang="java">

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;
 }

}</source>

3.0
2.0953333333333335
8.5

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

   <source lang="java">

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]);
 }

}</source>

Methods Accepting a Variable Number of objects

   <source lang="java">

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();
 }

}</source>

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

Overloading Vararg Methods

   <source lang="java">

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);
 }

}</source>

Use varargs with standard arguments.

   <source lang="java">

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: ");
 }

}</source>

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.

   <source lang="java">

int aMethod(int a, int b, double c, int ... vals) {}</source>

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