String Methods Flashcards
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
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!
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
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);
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$
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$
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
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
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);
charAt(index)
EXAMPLE:
Example
String str = “Java is fun.”;
char c = str.charAt(3);
System.out.println(c);
Expected output: a
toUpperCase()
EXAMPLE:
Example:
String str = “TechGloBAL”;
System.out.println(str.toUpperCase());
Expected output: TECHGLOBAL
toLowerCase()
EXAMPLE:
Example
String str = “JAvA is FuN”;
System.out.println(str.toLowerCase());
Expected output: java is fun
equalsIgnoreCase()
EXAMPLE:
Example
String str1 = “TechGlobal”;
String str2 = “TecHgLOBal”;
System.out.println(str1.equalsIgnoreCase(str2));
Expected output: true
equals()
EXAMPLE:
Example
String str1 = “Java”;
String str2 = “Hello”;
System.out.println(str1.equals(str2));
Expected output: false
concat()
EXAMPLE:
Example
String str = “Tech”;
String strNew = str.concat(“Global”);
System.out.println(strNew);
Expected output: TechGlobal
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
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
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
trim()
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)
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)
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)
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)
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)
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
- 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 - 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)
