Java variables from array

Java — Arrays

Java provides a data structure, the array, which stores a fixed-size sequential collection of elements of the same type. An array is used to store a collection of data, but it is often more useful to think of an array as a collection of variables of the same type.

Instead of declaring individual variables, such as number0, number1, . and number99, you declare one array variable such as numbers and use numbers[0], numbers[1], and . numbers[99] to represent individual variables.

This tutorial introduces how to declare array variables, create arrays, and process arrays using indexed variables.

Declaring Array Variables

To use an array in a program, you must declare a variable to reference the array, and you must specify the type of array the variable can reference. Here is the syntax for declaring an array variable −

Syntax

dataType[] arrayRefVar; // preferred way. or dataType arrayRefVar[]; // works but not preferred way.

Note − The style dataType[] arrayRefVar is preferred. The style dataType arrayRefVar[] comes from the C/C++ language and was adopted in Java to accommodate C/C++ programmers.

Example

The following code snippets are examples of this syntax −

double[] myList; // preferred way. or double myList[]; // works but not preferred way.

Creating Arrays

You can create an array by using the new operator with the following syntax −

Syntax

arrayRefVar = new dataType[arraySize];

The above statement does two things −

• It creates an array using new dataType[arraySize].
• It assigns the reference of the newly created array to the variable arrayRefVar.

Declaring an array variable, creating an array, and assigning the reference of the array to the variable can be combined in one statement, as shown below −

dataType[] arrayRefVar = new dataType[arraySize];

Alternatively you can create arrays as follows −

The array elements are accessed through the index. Array indices are 0-based; that is, they start from 0 to arrayRefVar.length-1.

Example

Following statement declares an array variable, myList, creates an array of 10 elements of double type and assigns its reference to myList −

double[] myList = new double[10];

Following picture represents array myList. Here, myList holds ten double values and the indices are from 0 to 9.

Processing Arrays

When processing array elements, we often use either for loop or foreach loop because all of the elements in an array are of the same type and the size of the array is known.

Example

Here is a complete example showing how to create, initialize, and process arrays −

public class TestArray < public static void main(String[] args) < double[] myList = ; // Print all the array elements for (int i = 0; i < myList.length; i++) < System.out.println(myList[i] + " "); >// Summing all elements double total = 0; for (int i = 0; i < myList.length; i++) < total += myList[i]; >System.out.println("Total is " + total); // Finding the largest element double max = myList[0]; for (int i = 1; i < myList.length; i++) < if (myList[i] >max) max = myList[i]; > System.out.println("Max is " + max); > >

This will produce the following result −

Output

1.9 2.9 3.4 3.5 Total is 11.7 Max is 3.5

The foreach Loops

JDK 1.5 introduced a new for loop known as foreach loop or enhanced for loop, which enables you to traverse the complete array sequentially without using an index variable.

Example

The following code displays all the elements in the array myList −

public class TestArray < public static void main(String[] args) < double[] myList = ; // Print all the array elements for (double element: myList) < System.out.println(element); >> >

This will produce the following result −

Output

Passing Arrays to Methods

Just as you can pass primitive type values to methods, you can also pass arrays to methods. For example, the following method displays the elements in an int array −

Example

public static void printArray(int[] array) < for (int i = 0; i < array.length; i++) < System.out.print(array[i] + " "); >>

You can invoke it by passing an array. For example, the following statement invokes the printArray method to display 3, 1, 2, 6, 4, and 2 −

Example

Returning an Array from a Method

A method may also return an array. For example, the following method returns an array that is the reversal of another array −

Example

public static int[] reverse(int[] list) < int[] result = new int[list.length]; for (int i = 0, j = result.length - 1; i < list.length; i++, j--) < result[j] = list[i]; >return result; >

The Arrays Class

The java.util.Arrays class contains various static methods for sorting and searching arrays, comparing arrays, and filling array elements. These methods are overloaded for all primitive types.

public static int binarySearch(Object[] a, Object key)

Searches the specified array of Object ( Byte, Int , double, etc.) for the specified value using the binary search algorithm. The array must be sorted prior to making this call. This returns index of the search key, if it is contained in the list; otherwise, it returns ( – (insertion point + 1)).

public static boolean equals(long[] a, long[] a2)

Returns true if the two specified arrays of longs are equal to one another. Two arrays are considered equal if both arrays contain the same number of elements, and all corresponding pairs of elements in the two arrays are equal. This returns true if the two arrays are equal. Same method could be used by all other primitive data types (Byte, short, Int, etc.)

public static void fill(int[] a, int val)

Assigns the specified int value to each element of the specified array of ints. The same method could be used by all other primitive data types (Byte, short, Int, etc.)

public static void sort(Object[] a)

Sorts the specified array of objects into an ascending order, according to the natural ordering of its elements. The same method could be used by all other primitive data types ( Byte, short, Int, etc.)

Источник

Set Variable from an Array directly into a List of Variables in Java

Solution 1: Java passes references by value so changes to objects referenced by them will be visible outside the method. Also slighty offtopic: for your particular case it would better to either use Map (mapping id of the animal to the quantity) or array or list of Solution 2: Some basics on object orientation: First create a class for your animals with fields for ID and Quantity.

Set Variable from an Array directly into a List of Variables in Java

Basically no, this isn’t possible.

You’ll have to return an object that contains the values.

MyObject myObject = calculateMyObject(); 

The only way would be using reflection, granted you know upfront how many items method «calculateSomeDouble» will return.

A variation of this would be needed. But as you see there’s more to code.

So the question that raises is? DO you want this for an automated stuff ? Or to save time for developing ( avoid having to copy/paste ) ?

If you want to automate some task ( like filling an object at runtime ) then it is worth to do the reflection call and write the method.

You will need to set the value rather than only print it.

The client call should look like

 SomeUtility.fill( myObject , withDoublesFromMethod() ); 

When you no that you get 2 double values back you can call your methode usig call by reference

You can submit a array with length 2 and put the values iside the methode.

Or you return a Collection if the returned values can change.

Ia m not the friend of returning values like

When you use Lists or Collections the methode is ot as static as you handle with arrays. You can better reuse the methode in other projects.

How to Return an Array in Java?, Here we will be considering three examples for scenarios. Case 1: Simple Built-in arrays. Case 2: Array of objects. Case 3: Returning multidimensional arrays. Case 1: Returning an integer (built-in data type) array in java. Any built-in data type’s array be integer, character, float, double all can be returned simply …

Android Function to return an array directly into variables

This is a rather basic question: Anyway :

In answer to the second part of the question, instead of

although its not very elegant it would assign the return value to each variable.

How to Return an Array in Java, How to return an array in Java. In this section, we are going to learn how to return an array in Java. Remember: A method can return a reference to an array. The return type of a method must be declared as an array of the correct data type. Example 1. In the following example, the method returns an array of integer type.

Assigning variables to array

Java passes references by value so changes to objects referenced by them will be visible outside the method. If you already have your arrays defined, you can simply write:

 void loadFromMySql(String tableName, int[] arrayA, int[] arrayB)

That of course won’t work if you want to create new arrays inside the method — in that case you have to create some wrapper object.

Also slighty offtopic: for your particular case it would better to either use Map (mapping id of the animal to the quantity) or array or list of

Some basics on object orientation:

First create a class for your animals with fields for ID and Quantity.

public class MyCustomAnimal < // field variables private int Id; private int Qty; // getter and setter public int getId() < return this.Id; >public void setId(int id) < this.Id = id; >public int getQty() < return this.Qty; >public void setQty(int qty) < this.Qty = qty; >// constructor public MyCustomAnimal(int id, int qty) < this.Id = id; this.Qty = qty; >> 

Then create objects of the type MyCustomAnimal from your database query.

MyCustomAnimal animal = new MyCustomAnimal(123, 4); 

Or even create an array of your animal objects.

MyCustomAnimal[] animal = new MyCustomAnimal[3]; animal[0] = new MyCustomAnimal(615, 7); animal[1] = new MyCustomAnimal(654, 5); animal[2] = new MyCustomAnimal(687, 9); 

Set Variable from an Array directly into a List of, When you no that you get 2 double values back you can call your methode usig call by reference. void methode (double [] array) You can submit a array with length 2 and put the values iside the methode. Or you return a Collection if the returned values can change. List methode () Ia m not the friend of returning …

Java Passing Variables and returning value

You don’t assign the result of the method to anything. Change your code to:

String errorMessage = checkValue(orderSplit); 

And not that the checkValue method doesn’t need any error message as argument. It will create one by itself and return it to the caller.

Also, assigning null to a variable you reassign immediately after, like this:

String[] orderSplit = null; orderSplit = order.split(" "); 

is unnecessary. You just need

String[] orderSplit = order.split(" "); 

And you should never compare Strings with == . == tests if two variables reference the same String object. You should use the equals() method, which tests if two Strings contain the exact same sequence of characters:

You aren’t assigning the return value of checkValue anywhere, only returning its parameter. Try changing

String errorMessage = ""; checkValue(orderSplit, errorMessage); 

String errorMessage = ""; errorMessage = checkValue(orderSplit, errorMessage); 

java.lang.String is immutable. So whatever you do to errorMessage inside your method will not be visible outside the method, as essentially you are creating new String objects.

You should really check the return value from the method as other answers suggest.

Java — Returning an array without assign to a variable, You still need to create the array, even if you do not assign it to a variable. Try this: public int [] getData () < return new int [] ; > Your code sample did not work because the compiler, for one thing, still needs to know what type you are attempting to create via static initialization <>. Share. Improve this …

Источник