Strings

Watch this video as support 👇

https://youtu.be/9R9nVa_MWPA

A string is a data type used for handling text. Strings are always sourrounded by double quotes. Here is an example:

String fruit = "banana";

The way a string is built up is as a sequence of characters. So the first character in fruit is b, the second character is a and so on. In programming languages the first element has index 0 (which is a bit weird in the beginning)

String character sequence

That means that if we wanted the first character in a string we would get that at index 0!

char firstCharacter = fruit.charAt(0);
System.out.println(firstCharacter); // prints b

String are different than the types we saw when working with int, double or char. String is called non primitive/complex data type. Lets get into the differences between primitive and non-primitive

Primitive data types

There are 8 primitive data types in java as you can in the figure below. Primitive data types is predefined by its language and holds the value of a variable directly in memory!

Primitive data types

Complex data types

This types has many names, it's also called reference types or complex types. Here the value of the some variable is not held in memory. Instead a reference to the object is held in memory!

There are some more differences that you will learn later. But one thing that is relevant now is that a String has methods that can be called on them.

To call a method on a String write . and then the method you want to call. Here is an example

String name = "Benjamin";
String upperCaseName = name.toUpperCase();
System.out.println(upperCaseName) // prints BENJAMIN

IntelliJ will autocomplete with methods when pressing . after a string variable as can be seen below

String methods

To find more methods see here: https://www.w3schools.com/java/java_ref_string.asp

Lets see some more examples

String lastname = "Hughes";
lastname.toUpperCase(); // HUGHES
lastname.charAt(2); // g
lastname.length(); // 6

//We can even add strings together:
String firstname = "Benjamin ";
String lastname = "Hughes";
String fullname = firstname + lastname;
System.out.println(fullname); // Benjamin Hughes

Exercises

Exercise 1

In a group investigate two different string methods.

You need to be able to explain what the method does but also how to use it in Java!

A couple of groups will be selected to show what they learned

Execise 2

• Convert a string to uppercase

• Return the index of a character

• Concatenate two different string

• Check these strings are equal to each other. Uppercases should be ignored!

  • hello, ollhe should print false

  • bike, banana should print false

  • name, NaMe should print true

  • yes, yes should print true

Exercise 3

Løs de her opgaver: https://www.w3resource.com/java-exercises/string/index.php

1, 7, 8, 22

Exercise 3.1

Create a java program that takes a string and a substring as input. The program should then check if the substring is part of the string 👇

Please input a string:
benjamin
Please input a substring to check:
jam
Is jam is part of Benjamin? true

Please input a string:
Camilla
Please input a substring to check:
was
Is was is part of Camilla? false

Alternatively you can write it like this (if you know if sentences):

Please input a string:
benjamin
Please input a substring to check:
jam
jam is part of Benjamin

Please input a string:
Camilla
Please input a substring to check:
put
put is not part of Camilla

Ask your classmates about an if sentence!

Exercise 3.11

Write a program that takes a three character string as input and checks if the string is mirrored. The case should be ignored. fx Lol should return true

Here is an example

Please input a word:
lok
Can lok be mirrored: false

Please input a word:
lol
Can lol be mirrored: true

You can again write different messages if you know if sentences

Exercise 3.21

Write a program that can check if a number is even.

Now write a program that will check if a number is odd.

Hint: Read up on modulus!

Exercise 3.3

Write a program that takes two numbers. One that that decides the diviser and one that is the number that should be checked against the divider:

Example

Please put in the diviser:
5
Now please put in the number to check
35
Is 35 divisible with 5: true

Please put in the diviser:
6
Now please put in the number to check
13
Is 13 divisible with 6: false

Exercise 🏎

Write a program that will check if the first character in a word comes later in the alphabeat than the last character in word

Example

Please write a word:
jungle
j comes after e in the alphabeat

Please write a word:
Bananas
B comes before s in the alphabeat

Exercise 🍌

Write a Java program that accepts a 3 digit integer n and compute the sum of the digits of n

Example:

Please input a number: 
334
The sum of 3 and 4 and 4 is 10

Please input a number: 
121
The sum of 1 and 2 and 1 is 4

Exercise 🥁

Løs de her opgaver: https://www.w3resource.com/java-exercises/string/index.php

2, 3, 25