Difference between revisions of "Java/C2/Array-Operations/English"

Welcome

Learning Outcomes

import the class Arrays and,

perform basic operations on arrays.

Tools Used

Ubuntu 11.10,

JDK 1.6 and

Eclipse 3.7.0

Prerequisites

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import java.util.Arrays;

To access them, we need to import that class.

It is done by the statement import java.util.Arrays;.

We can access a method from the class.

We do it by adding a dot and the method name.

So Arrays dot toString means toString method from the class Arrays.

Minimize Slides and open Eclipse

{Eclipse should contain the following code}

public class ArraysDemo{

public static void main(String[] args){

}

}

We have already created a class ArraysDemo.

Let us now import the class Arrays.

import java.util.Arrays;

Before public class, type

import java.util.Arrays

This statement says that java contains a package called util which contains the class Arrays and it has to be imported.

int marks[] = {2, 7, 5, 4, 8};

Inside the main function,type

int marks open close square brackets equal to within brackets 2, 7, 5, 4, 8 semicolon.

String mStr = Arrays.toString(marks);

System.out.println(mStr);

Type String mStr equal to Arrays dot toString within brackets marks semicolon.

The toString method gives a string representation of the array.

Now, we shall print the marks.

So, type System dot out dot println within brackets mStr semicolon.

Now let us run it.

Now let us look at sorting the elements of the array.

Arrays.sort(marks);

Highlight sort.

The sort method in the Arrays class, sorts the elements of the array passed to it.

Now we are sorting the array and then printing the string form of it.

Let us look at the output.

Note that the sort method has changed the array itself.

This type of sorting is called inplace sorting.

It means the array which contains the elements is changed as a result of sorting.

The next method we are going to look at, is fill

Arrays.fill(marks, 6);

The first is the array to fill and the second is what should it be filled with.

Remove the sorting line and

Type Arrays dot fill within brackets marks, 6;

Now let us look at the output.

The next method we are going to look at, is copyOf

int marksCopy[];

Type int marksCopy[];

marksCopy = copyOf(marks, 5);

Change toString(marks) to toString(marksCopy)

The copyOf method takes two arguments.

The first argument is the array to copy from.

And the second is the no.of elements to copy.

Now let us look at the contents of the new array.

We see that the elements of the array marks have been copied to the array marksCopy.

Change 5 to 3

Let us now look at the new array.

As we can see, only the first three elements have been copied.

Let us see what happens if the no.of elements to be copied is greater than the total no.of elements in the array.

save and run. Point to output

Save and Run the program

As we can see, the extra elements have been set to the default value, which is 0.

Next we'll see how to copy a range of values.

copyOfRange(marks, 1, 4) copies all the elements starting from index 1 and stopping at index 3.

Now let us look at the output.

As we can see, the elements from index 1 to index 3 have been copied.

Note that we have given 1, 4 in the method.

But even, then the element at index 4 has not been copied.

Only the elements till index 3 have been copied.

(0, 4) implies from index 0 to index 3

(4, 6) implies from index 4 to index 6

So it behaves as if (0, 4) + (4, 6) = (0, 6)

Slide 6

Summary

In this tutorial we have learnt

how to import the class Arrays.

Perform array operations like sort and copy.

Read about the Arrays.equals method and find out what is does.

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