String Methods Flashcards by Torrie Green

valueOf()

Method Task: Convert given variable to a String

    - it is static - you can cll it with class name
    - it is a return type, and it returns a string
    - it takes different arguments as it is an overloaded method and converts given args to a String

int i = 5;

    String num = String.valueOf(i); // num  = 5
    System.out.println(i + i);// 10
    System.out.println(num+num);// 55

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concat()

Method Task: It is used to combine multiple strings and form a new one

    - it is non-static, and we can call it with an object created
    - it is a return type method, and it returns a new String that is the combination of the others
    - it takes a String as an argument      

    String s1 = "Tech"; // String object
    String s2 = "Global"; // String object

    String s3 = s1.concat(s2); // String s3 = s1 + s2; // TechGlobal

    System.out.println(s3.concat(" School")); // TechGlobal School

    System.out.println("Hello".concat(" World!")); // Hello World!
    System.out.println("Hello".concat(" ").concat("World!")); // Hello World!
    System.out.println("Hello".concat(" ") + "World!"); // Hello World!

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equals()

Method Task: It compares 2 strings with each other and tells if they are equal or not
NOTE: this comparison is case-sensitive
-it is non-static, and we call it with another String object
-it is a return type and returns a boolean
-it takes a String as an argument

    System.out.println("Melda".equals("Melda")); // true
    System.out.println("melda".equals("Melda")); // false

    String name1 = "John";
    String name2 = "James";
    String name3 = "James";

    System.out.println(name1.equals(name2)); // false
    System.out.println(name2.equals(name3)); // true

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equalsIgnoreCase()

Method Task: It compares 2 strings with each other and tells if they are equal or not
NOTE: This comparison is case-insensitive
-It is non-static, and we call it with another String object
-It is a return type and returns a boolean
-It takes a String as an argument

    System.out.println("Hello".equals("hello")); //false
    System.out.println("Hello".equalsIgnoreCase("hello")); // true
    System.out.println("Hello".equalsIgnoreCase(" hello")); // false

    String s1 = "Good";
    String s2 = "GOOD";

    boolean b = s1.equalsIgnoreCase(s2); // true
    System.out.println(b);

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toLowerCase()

Method Task: These methods are used to convert letters of a String to uppercase or lowercase

    - They are non-static methods that you can call them with objects of String class
    - They are return type methods, and they return the modified String object back
    - They don't take any argument

    String s1 = "HELLO world 10$";

    System.out.println(s1); // HELLO world 10$
    System.out.println(s1.toLowerCase()); // hello world 10$
    System.out.println(s1.toUpperCase()); // HELLO WORLD 10$

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toUpperCase()

Method Task: These methods are used to convert letters of a String to uppercase or lowercase

    - They are non-static methods that you can call them with objects of String class
    - They are return type methods, and they return the modified String object back
    - They don't take any argument

    String s1 = "HELLO world 10$";

    System.out.println(s1); // HELLO world 10$
    System.out.println(s1.toLowerCase()); // hello world 10$
    System.out.println(s1.toUpperCase()); // HELLO WORLD 10$

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charAt(index)

Method Task: it helps to get a character at a specific index
NOTE: index starts with zero
-it is non-static as we call it with object name
-it is a return type and returns char primitive
-it takes an argument which is int index
NOTE: It will throw StringIndexOutOfBoundsException when the given index is not in the bounds

    String name = "John";

    System.out.println(name.charAt(0));//J
    System.out.println(name.charAt(1));//o
    System.out.println(name.charAt(2));//h
    System.out.println(name.charAt(3));//n

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indexOf(anyChar)

indexOf(anyString)

Method Task:They are used to find the index or last index of some char or String values in another String
-They are non-static methods and called with another String object
-They are return type, and they return int as index
-They take either String or char as arguments
NOTE: if the given char or String does not exist, then they return -1
NOTE: if you are looking for an index of String, and it exists, it will return the first index of found match
EXAMPLE: sentence.indexOf(“Chicago”); // 7

    String sentence = "I like Chicago and Miami more than any other cities";

    System.out.println(sentence.indexOf('C'));//7
    System.out.println(sentence.indexOf('c'));//10
    System.out.println(sentence.lastIndexOf('c'));//45

    sentence. indexOf("Chicago"); // 7
    sentence. indexOf("Miami"); // 19
    sentence. indexOf("Florida"); // -1
    sentence. indexOf("Florida"); // -1

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indexOf(anyChar)
indexOf(anyString)

EXAMPLE:

String str = “TechGlobal”;

int indexOfLetterG = str.indexOf(‘G’);

int indexOfGlobalWord = str.indexOf(“Global”);

System.out.println(indexOfLetterG);

System.out.println(indexOfGlobalWord);

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charAt(index)

EXAMPLE:

Example
String str = “Java is fun.”;
char c = str.charAt(3);
System.out.println(c);

Expected output:
a

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toUpperCase()

EXAMPLE:

Example:
String str = “TechGloBAL”;
System.out.println(str.toUpperCase());

Expected output:
TECHGLOBAL

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toLowerCase()

EXAMPLE:

Example
String str = “JAvA is FuN”;
System.out.println(str.toLowerCase());

Expected output:
java is fun

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equalsIgnoreCase()

EXAMPLE:

Example
String str1 = “TechGlobal”;
String str2 = “TecHgLOBal”;

System.out.println(str1.equalsIgnoreCase(str2));

Expected output:
true

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equals()

EXAMPLE:

Example
String str1 = “Java”;
String str2 = “Hello”;
System.out.println(str1.equals(str2));

Expected output:
false

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concat()

EXAMPLE:

Example
String str = “Tech”;
String strNew = str.concat(“Global”);
System.out.println(strNew);

Expected output:
TechGlobal

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valueOf()

EXAMPLE:

Example
int number = 125;
boolean check = true;
String strNumber = String.valueOf(number);
String strCheck = String.valueOf(check);
System.out.println(strNumber);
System.out.println(strCheck);

Expected output:
 125
true

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indexOf(int ch)

lastIndexOf(int ch)

Method Task: They are used to find the index or last index of some char or String values in another String
-They are non-static methods and called with another String object
-They are return type, and they return int as index
-They take either String or char as arguments
NOTE: if the given char or String does not exist, then they return -1
NOTE: if you are looking for an index of String, and it exists, it will return the first index of found match

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length()

Method Task: Count the total number of the characters in a String and return it as an int
-It is a non-static method and can be called with object name
-It is a return type method, and it returns an int (total number of characters)
-It does not take any arguments
NOTE: It is like human thinking - HOW MANY

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trim()

Study These Flashcards

Method Task: It is used to remove whitespaces from both ends of a String
-it is non-static, and we call it with an object name
-it is return type and return a String
-it does not take any argument
NOTE: trim() method will not remove any extra space between the words,
it only removes extra spaces before and after the first and last chars in the String

substring(int beginIndex)

Study These Flashcards

Method Task: They are used to extract a substring from a larger string
-They are non-static, and we call them with objects
-They are return type, and they return another string
-There are 2 overloaded substring methods
1. substring(int beginIndex)
-This method takes begin index as an argument, and it extracts a substring starting from given index
to the end

substring(int beginIndex, int endIndex)

Study These Flashcards

Method Task: They are used to extract a substring from a larger string
-They are non-static, and we call them with objects
-They are return type, and they return another string
-There are 2 overloaded substring methods
2. substring(int beginIndex, int endIndex)
-This method will take 2 args to define which index to start and which index to stop to extract
a substring
NOTE: beginIndex is inclusive but endIndex is exclusive
NOTE: if your beginIndex is equal to endIndex, then it will return empty string
NOTE: if beginIndex is less than endIndex, then it will throw StringIndexOutOfBoundsException

startsWith(String prefix)

endsWith(String suffix)

Study These Flashcards

Method Task: They are used to finding out if the string starts with or ends with another letter or string

    - They are non-static as we call them with objects
    - They return boolean
    - They take String as an argument

contains(CharSequence s)

Study These Flashcards

Method Task: It is used to find out if a String contains another string or character

    - It is non-static, and we can call it with an object
    - it is a return type, and it returns a boolean
    - It takes a String argument

replace(char oldChar, char newChar)

replace(CharSequence target, CharSequence replacement)

Study These Flashcards

Method Task: It is used to replace some values in a String with another value
NOTE: it replaces all the occurrences.
-it is non-static
-it is a return type and returns another which is modified
-it takes 2 arguments (char or String)

isEmpty()

Method Task: It is used to check if a given string is empty or not - it is non-static, and we call it with an object - it is a return type, and it returns a boolean - it does not take any arguments

substring() | EXAMPLE:

String sentence = ScannerHelper.getASentenceFromUser(); String first = sentence.substring(0,sentence.indexOf(' ')); String last = sentence.substring(sentence.lastIndexOf(' ')+1); System.out.println("The first word is = '"+ first + "'"); System.out.println("The last word is = '"+ last+"'");

Given a string, return a version without the first and last char, so "Hello" yields "ell". The string length will be at least 2.

String str = "hello" | return str.substring(1 , str.length( )- 1); // ell

Index Error

StringIndexOutOfBoundsException

Find the last character:

String word = "tenacity"; word.charAt(word.length()-1); // y

Find the first character:

String word = "tenacity"; word.charAt(0); // t

Find the last 3 characters:

String word = "tenacity"; word.substring(word.length()-3);

Find the first 3 characters:

String word = "tenacity"; word.substring(0,3)

Find the last word:

String sentence = "java is fun" sentence.substring(sentence.lastIndexOf(' ')+1);

Find the first word:

String sentence = "java is fun"; sentence.substring(0 , sentence.indexOf(' '));

contains() EXAMPLE:

Example String str = “TechGlobal”; boolean checkIfStrContainsGlo = str.contains(“Glo”); System.out.println(checkIfStrContainsGlo); Expected output: true String s = "Good Morning"; s. contains("Good"); // true s. contains("good"); // false

replace() EXAMPLE:

Example String str = “TechGlobalo”; String capitalizeAllOLetters= str.replace(‘o’, ‘O’); String removeTech = str.replace(“Tech”, “”); System.out.println(capitalizeAllOLetters); Expected output: TechGlObalO String s = "banana"; System.out.println(s.replace('a' , '$'));

isEmpty() EXAMPLE:

Example String str = “”; boolean isStrEmpty= str.isEmpty(); System.out.println(isStrEmpty); Expected output: true String name = "John"; System.out.println(name.isEmpty()); // false System.out.println(name.replace(name, "").isEmpty()); // true

Method Chaining

if the chained method goes inside the argument you must add the object before the dot example: word.charAt(word.length()-1); if the chained method does NOT go inside the argument it does NOT get an object before the dot example: word.toLowerCase().charAt(0);

A method is...

- It is also a function - Every method will have a task to execute when it is invoked - Reusable

THERE ARE 2 TYPES OF METHODS IN JAVA

1. void methods - does not return anything but executes a block of code - return keyword cannot be used with this method - can be created with void keyword - void methods can be static or non-static 2. return type methods - does return something - return keyword MUST be used, otherwise it is a compiler error - cannot use void keyword - return type methods can be static or non-static NOTE: Each time you invoke a method, all the code block will be executed

METHOD COMPONENTS syntax:

``` accessModifier returnType methodName(){ // the body goes here } ```

METHOD COMPONENTS Access Modifiers:

``` accessModifier returnType methodName(){ // the body goes here } ``` access modifiers: PUBLIC -> anywhere in the project DEFAULT -> only in the same package ``` PRIVATE -> only same class PROTECTED -> we will learn later ```

METHOD COMPONENTS Return Type:

``` accessModifier returnType methodName(){ // the body goes here } ``` returnType -It specifies what type of value a method returns. For example, if a method has an int return type then it returns an integer value -If the method does not return a value, its return type is void

Get the 2 middle letters if an even lettered name

"" + str.charAt(str.length()/2-1) + str.charAt(str.length()/2)

Get the middle letter if an odd lettered name

"" + str.charAt(str.length()/2)

String Methods Flashcards

(45 cards)