What is an argument list in java

Java Program to Pass ArrayList as the function argument

In this article, we will understand how to pass ArrayList as the function argument. The ArrayList class is a resizable array, which can be found in the java.util package. The difference between a built-in array and an ArrayList in Java, is that the size of an array cannot be modified.

Below is a demonstration of the same −

Suppose our input is −

The desired output would be −

The list is defined as: Java Python Scala Mysql Redshift

Algorithm

Step 1 - START Step 2 - Declare namely Step 3 - Define the values. Step 4 - Create an ArrayList, and iterate over it, and display it. Step 5 - In the main method, create the ArrayList, and add elements to it using the ‘add’ method. Step 6 - Display this on the console. Step 7 - Stop

Example 1

Here, we iterate a string array list.

import java.util.ArrayList; public class Demo < public static void print(ArrayListinput_list) < System.out.print("\nThe list is defined as:\n "); for(String language : input_list) < System.out.print(language + " "); >> public static void main(String[] args) < System.out.println("The required packages have been imported"); ArrayListinput_list = new ArrayList<>(); input_list.add("Java"); input_list.add("Python"); input_list.add("Scala"); input_list.add("Mysql"); input_list.add("Redshift"); print(input_list); > >

Output

The required packages have been imported The list is defined as: Java Python Scala Mysql Redshift

Example 2

Here, we iterate an integer array list.

import java.util.ArrayList; public class Demo < public static void print(ArrayListinput_list) < System.out.print("\nThe list is defined as:\n "); for(Integer elements : input_list) < System.out.print(elements + " "); >> public static void main(String[] args) < System.out.println("The required packages have been imported"); ArrayListinput_list = new ArrayList<>(); input_list.add(500); input_list.add(600); input_list.add(700); input_list.add(800); input_list.add(950); print(input_list); > >

Output

The required packages have been imported The list is defined as: 500 600 700 800 950

Источник

Java arguments in java methods are code example

Arguments Parameters It is used to send values from the calling method to the receiving method They are defined when the function is defined It is also known as actual parameter or actual argument It is also known as a formal parameter or formal argument An argument is a nameless expression that can be a variable, a constant, or a literal. Output: Differences between Arguments and Parameters in Java In this section, we will tackle the differences between arguments and parameters.

Parameters vs Arguments in Java

This tutorial introduces the difference between parameters and arguments with examples in Java.

Parameters and arguments are the most used terms in computer programming. Whenever we write a program, there is a high probability of using a function/method. The concept of the method has two terms associated with it, the first is the arguments, and the second is parameters.

In this tutorial, we will discuss arguments and parameters in detail.

What are Parameters in Java

Parameters are the variables that are present in the method definition. We use these variables inside the method for data manipulations.

The parameters have local scope as they can only be used in the method. These variables make the method’s execution easier. Let’s see an example to understand what we’re talking about:

public int multiply(int par1, int par2)

In the example code above, par1 and par2 are the parameters of the method multiply() . These are two local variables having a function-specific lifespan. They can also accept any values passed to the method when it’s called.

What are Arguments in Java

The variables provided to the method during calling for execution are called arguments.

Furthermore, the method’s local variables take the values of the arguments and can thus process these parameters for the final output. The arguments are the real values we provide as input to obtain the desired result.

Let’s see an example to understand what we’re talking about:

public static void main(String args[]) < int arg1 = 90; int arg2 = 50; int r = multiply(arg1, arg2); // arg1 and arg2 are the arguments for this method >

In the example code above, arg1 and arg2 are the arguments. Since arguments are real values, in our example, 90 and 50 are used as arguments values.

Let’s understand with a complete example.

public class SimpleTesting < public static void main(String args[]) < int arg1 = 90; int arg2 = 50; int r = multiply(arg1, arg2); // arg1 and arg2 are the arguments System.out.println("result = "+r); >public static int multiply(int par1, int par2) < int result = par1 * par2; return result; >> 

Differences between Arguments and Parameters in Java

In this section, we will tackle the differences between arguments and parameters. To better understand, look at the table below. We provide a summarized comparison here.

Arguments	Parameters
It is used to send values from the calling method to the receiving method	They are defined when the function is defined
It is also known as actual parameter or actual argument	It is also known as a formal parameter or formal argument
An argument is a nameless expression that can be a variable, a constant, or a literal.	A parameter has a name, a data type, and a method of being called (call by reference or call by value)

Important points

• The total number of parameters in a method definition should match the number of arguments in a method call. The method with variable-length parameter lists is an exception to this rule.
• In a method call, the data type of arguments should match the data type of parameters in the method specification.

Conclusion

In this article, we learned what arguments and parameters are. Argument and parameter are frequently used interchangeably. We now know what both of these terms exactly mean in Java programming.

Java Parameter

Java Varargs | Java Variable Arguments, Java Varargs | Java Variable Arguments — The varrags allows the method to accept zero or muliple arguments. Before varargs either we use overloaded method or take an array as the method parameter but it was not considered good because it leads to the maintenance problem. If we don’t know how many argument we will have …

Generic method arguments

Can getA and getB be combined into a single interface method?

Now, you can simply call getIndex , and your method signature will be:

public Integer getHighestIndexValue(List list) 

As a side note, if you define your interface to extend Comparable i.e.:

interface ProvidesIndex extends Comparable

Then you can use Collections.max directly on the initial list:

List list = new ArrayList(); list.add(new ObjectA()); list.add(new ObjectB()); Integer max = Collections.max(list).getIndex(); 

Adding to the answer by Raman :

public Integer getHighestIndexValue(List list) < int highestValue; Listindexes = new ArrayList(); for (CommonInterface a: list) < indexes.add(Integer.parseInt(a. getIndex())); >highestValue = Collections.max(indexes); return highestValue; > 

Guava has an elegant solution to this:

//general purpose function to get A, can be used in transform(), etc private static final Function GET_A = new Function<>() < @Override public Integer apply(ObjectA a) < return a.getA(); >> Integer highestIndex = Collections.max(Collections2.transform(list, GET_A)); 

Or, if you need the element with the highest index,

ObjectA highest = Ordering.natural().onResultOf(GET_A).max(list); 

Then to extend this to ObjectB you just need to implement a GET_B function.

Going back to your helper method (which is basically irrelevant now that you have a one-liner):

public Integer getHighestIndex(List list, Function indexPlucker)

Arguments in java methods are: Code Example, public static void hello (String hey, String wassup) //the paramter in this case is located in the parenthesis

Provide arguments with a method

If the number of parameters is fixed at the call site, you could use varargs

otherwise you’d use an array or collection

You can then of course have another method provide the value of these parameters:

Varargs

Java has a built-in feature to denote a variable length of arguments. It is called varargs (documentation) (variable arguments) and it only works if the type stays the same . The syntax for a method is like this:

Note the int. values which denotes varargs . A caller can now call the method like

add(null) // Passing null add(values) // Passing an int[] add() // No arguments add(a) // One int add(a, b) // Two ints add(a, b, c) // Three ints add(a, b, c, d) // Four ints . 

Note the three special cases null , int[] and empty .

What Java does is it will convert the arguments into an array . So inside the method values will be a regular int[] . You could thus implement the method like

public int add(int. values) < int sum = 0; for (int value : values) < sum += value; >return sum; > 

If you, as a caller, want to pass the return value of a function you just need to make sure that it returns an array like int[] . So the following would work:

int sum = add(valueProvider()); 

Collection, Iterable and Stream

Besides that, if you don’t want to use varargs or arrays , you can use Collection s (documentation). A collection may be a List or a Set and so on. For example you could declare

public int add(Collection values) 

Collection values = new ArrayList<>(); values.add(1); values.add(2); int sum = add(values); 

An Iterable , in contrast to Collection would even be more flexible.

Using a Stream (documentation) would also work like a charm and is probably one of the most flexible variants since the source of a stream could be anything and nearly anything of the standard library supports a stream representation.

Changing type

Now note that what you searched for in the beginning, a method that is able to feed arbitrary arguments, is not possible in Java.

The main problem is that the types may change, so you may have a method like

public void doSomething(int first, String second, File third) 

and you won’t be able to feed the method with varargs, Collections or any of the presented methods.

In that case you will need a wrapper class like

public class DoSomethingArguments < private int mFirst; private String mSecond; private File mThird; public DoSomethingArguments(int first; String second, File third) < this.mFirst = first; this.mSecond = second; this.mThird = third; >// Some getters > 

(or a generic tuple class, a triple in this case)

But then you would need to change the method to

public void doSomething(DoSomethingArguments arguments) 

what is probably not what you wanted since you probably intended to not change the signature of doSomething .

But unfortunately there is no way to feed a method like this in such a way.

There is nothing that works the way you wish for at compile time. As the other answers are pointing out, there are varargs . But that is just syntactical sugar. That is just the compiler implicitly creating an array of a certain type for you.

But beyond that, there is reflection . Reflection allows you to dynamically inspect classes and methods at *runtime.

In other words: you can do something like

Object whatever = . Class someClass = whatever.getClass(); 

And now you can ask someClass about the methods it has. And which parameters they need.

But as said: all of that is runtime only. And it the reflection APIs are very easy to get wrong. And you only find out at runtime, when some exception is thrown.

Command Line arguments in Java programming, A command-line argument is an information that directly follows the program’s name on the command line when it is executed. To access the command-line arguments inside a Java program is quite easy. They are stored as strings in the String array passed to main ( ). Example

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