Strings
"Strings represent a sequence of characters."
Example
String name = "Hello World"
// String in-built functions
String.length()
This function is used to calculate the length of a string and the output is a int.
Example
String name = "Hello World";
int length = name.length();
System.out.println(length);
Output - 12
String.concat()
This function is used to concatinate 2 strings , second string at the end of first string.
Example
String start = "Hello";
String end = "World";
String concat = start.concat(end);
System.out.println(concat);
Output
HelloWorld
string.split()
This method is used to convert a string to an array based on regex value.
Example
String name = "You are a amazing person";
String[] words = name.split(" "); // Split based on space
for(String s : words){
System.out.println(s);
}
Output
You are a amazing person
String.toLowerCase()
This method converts all the characters in a string to lower case.
Example
String name = "Hello";
System.out.println(name.toLowerCase());
Output
hello
String.toUpperCase()
This method converts all the characters to upper case.
Example
String name = "Hello";
System.out.println(name.toUpperCase());
Output
HELLO
String.substring()
This method gives a substring of a string
Example 1
String name = "Hello World";
String sub = name.substring(2, 12);
System.out.println(sub);
Output
llo World
Example 1
String name = "Hello World";
String sub = name.substring(3);
System.out.println(sub);
Output
lo World
# Java Arrays
Arrays are used to store multiple values in a single variable, instead of declaring separate variables for each value.
To declare an array, define the variable type with square brackets:
String[] cars;
We have now declared a variable that holds an array of strings. To insert values to it, we can use an array literal - place the values in a comma-separated list, inside curly braces:
Example1
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
Example2
int[] myNum = {10, 20, 30, 40};
You can also create an array using the new keyword.
String[] name = new String[size];
Where size is the number of elements to be present Access the Elements of an Array:
You access an array element by referring to the index number.
Example
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
System.out.println(cars[0]);
Outputs
Volvo
Note:
Array indexes start with 0: [0] is the first element. [1] is the second element, etc.
Change an Array Element:
To change the value of a specific element, refer to the index number:
Example
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
cars[0] = "Opel";
System.out.println(cars[0]);
Now outputs Opel instead of Volvo
Array Length
To find out how many elements an array has, use the length property:
Example
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
System.out.println(cars.length);
Output
4
Loop Through an Array
You can loop through the array elements with the for loop, and use the length property to specify how many times the loop should run. The following example outputs all elements in the cars array:
Example
String[] cars = {"Volvo", "BMW", "Ford", "Mazda"};
for (int i = 0; i < cars.length; i++) {
System.out.println(cars[i]);
}
Output
Volvo BMW Ford Mazda
Multidimensional Arrays:
Two Dimensional Arrays
A Two Dimensional array is an array containing one or more 1-D arrays.
To create a two-dimensional array, add each array within its own set of curly braces:
Example:
int[][] twoDimen = {
{10, 20, 30, 40, 50},
{20, 30, 40, 50, 60},
{30, 40, 50, 60, 70}
};
To access the elements of the twoDimen array, specify two indexes: one for the row and the other for the column.
Example:
int[][] myNumbers = { {1, 2, 3, 4}, {5, 6, 7} };
int x = myNumbers[1][2];
System.out.println(x);
Output
7
Access the elements of 2D array using for loop
Example:
public class TestDrive {
public static void main(String[] args) {
int[][] twoDimen = {
{10, 20, 30, 40, 50},
{20, 30, 40, 50, 60},
{30, 40, 50, 60, 70}
};
for (int students = 0; students < 3; students++) {
for (int marks = 0; marks < 5; marks++) {
System.out.print(twoDimen[students][marks] + " ");
}
System.out.println();
}
}
}
/*
Subjects
sub0 sub1 sub2 sub3 sub4
Student 0 10 20 30 40 50
Student 1 20 30 40 50 60
Student 2 30 40 50 60 70
*/
`
Output
10 20 30 40 50
20 30 40 50 60
30 40 50 60 70
3D arrays
A Three Dimensional array is an array containing one or more 2D arrays.
Example
Suppose if you have represent 3 departments, which will have 2 students each and their respective marks in 3 subjects
int[][][] threeDimen = {
{
{
10, 20, 30
}, //Electronics Department
{
20, 40, 80
}
},
{
{
10, 25, 65
}, // CS Department
{
60, 70, 80
}
},
{
{
10, 21, 55
},
{ //Mech Department
62, 40, 10
}
}