Topic 3 String Part I

7/30/2019 Topic 3 String Part I

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Programming Language (JAVA)

Unit 6.5 String Manipulation

Presentation 1


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Objectives

At the end of this presentation, you will be able to:

Declare and manipulate strings List various string methods and their usage


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Introduction

A string is a sequence of characters.


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String Declaration

Example 1

char str [ ] = {'a','e','i','o','u'};


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String Declaration

Example 2

char text[ ] = {'I','','C','A','N','','W','R','I','T',

'E','A','','G','O','O','D','','P','R','O','G','R','A','

M','I','N','','J','A','V','A'};

Example 3

String text = "I CAN WRITE A GOOD

PROGRAM IN JAVA";


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String Class

String class is present in java.lang package.

The methods in this class are used to

manipulate strings.

The string objects created in a String class

cannot be changed.


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Creating String Object

Example 1

String s = new String( );

Syntax

String stringobject = new String( );


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Example 2

char arr[ ] = {'H','E','L','L','O'};

String s = new String(arr);

Syntax

String stringobject = new String(array_name);


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Example 3

char arr[ ] = {'H','E','L','L','O'};

String s = new String(arr);

String s1 = new String(s);

Syntax

String stringobject = new

String(stringobject);


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Example 4

String s = "I have to study for my exams";

Syntax

String stringobject = ;


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Hands-On!

Program stringdemo.java will declare string

objects and display the strings.


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String Methods

The String class has several methods that

can be used to manipulate the string values.

Each method has its own characteristic.


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length() method

Is used to find the number of characters in a

string.


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length() method

Example 1

String s = "I am going to school";

int numchar = s.length( );

System.out.println(numchar);

Output

20


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length() method

Example 2

String s = " ";

int numchar = s.length( );

System.out.println(numchar);

Output

2


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length() method

Syntax

int variable_name = stringobject.length( );


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Hands-On!

Program strlen.java will find the length of the

given string.


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concat() method

Example 1

String firststring = "The Twin Tower";

String secondstring = " looks beautiful";

String thirdstring =

firststring.concat(secondstring);

Output

The Twin Tower looks beautiful


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concat() method

Syntax

String Stringvariable3 = stringvariable1.concat

(stringvariable2);


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concat() method

Example 2

String s1 = "Result: "+5+1;

System.out.println(s1);

Output

Result: 51


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concat() method

Example3

String s2 = "Result: "+(5+1);

System.out.println(s2);Output

Result: 6


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Hands-On!

Program strconcat.java will illustrate the use

ofconcat() method.


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charAt() method

Extracts a single character from a string


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charAt() method

Example

String s = "Malaysia"

char ch = s.charAt(4);

System.out.println(ch);

Output

y


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charAt() method

Syntax

char variablename =

stringobject.charAt(int where);


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Hands-On!

Program extractchar.java will illustrate the

use ofcharAt() method.


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equals() method

Compares two strings for equality.


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equals() method

Example

String s1="Both are equal";

String s2="Both are equal";String s3="Both are not equal";

System.out.println(s1.equals(s2));

System.out.println(s1.equals(s3));

Output

true

false


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equals() method

Syntax

boolean variablename =

stringobject.equals(stringobject);


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Hands-On!

Program equalsdemo.java will compare two

string and return the value based on the

result.


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indexOf() method

Will search the first occurrence of a character

or set of characters inside a string.


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Example 1

int val1 = s.indexOf('s');

System.out.println(val1);

Output3

indexOf() method


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indexOf() method

Example 2

int val2 = s.indexOf("is");


Output2


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indexOf() method

Syntax

int variablename =

stringobject.indexOf(character);

int variablename =

stringobject.indexOf(string);


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lastIndexOf() method

Will search the last occurrence of a character

or a set of characters inside a string.


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Example 1

int val1 = s.lastIndexOf('s');


Output12



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Example 2

int val2 = s.lastIndexOf("is");


Output5


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Syntax

int variablename =

stringobject.lastIndexOf(character);int variablename =

stringobject.lastIndexOf(string);


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Hands-On!

Program occurstr.java will to illustrate the use

indexOf() and lastIndexOf() method.


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replace() method

Will replace all occurrences of a character in

a string with another character.


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replace() method

Example

String s="Hewwo";

String s1 = s.replace('w','l');

System.out.println(Old string= + s);

System.out.println(New string= + s1);

Output

Hello


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replace() method

Syntax

String stringvariable =

stringobject.replace(original,replacement);


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Hands-On!

Program repchar.java will illustrate the use of

replace() method.


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trim() method

Will trim the leading and trailing white spaces

in a string.


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trim() method

Example

String s=" Hello Malaysia ";

String s1 = s.trim( );


Output

Hello Malaysia


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trim() method

Syntax

String stringvariable = stringobject.trim( );


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Hands-On!

Program trimspace.java will illustrate the

use oftrim() method.


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toLowerCase() method

Converts all the characters in a string from

uppercase to lowercase.


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Example

String s1="LOWER";

String s2 = s1.toLowerCase( );


Output

lower


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Syntax


stringobject.toLowerCase( );


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toUpperCase() method

Converts all the characters in a string from

lowercase to uppercase.


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Example

String s1="upper";

String s2 = s1.toUpperCase( );


Output

UPPER


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Syntax


stringobject.toUpperCase( );


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Hands-On!

Program convertstring.java will illustrate the

use oftoLowerCase() and toUpperCase()

methods.


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substring() method

Extracts a part of the string.


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substring() method

Example

String s1="I do shopping in Mega Mall";

String s2 = s1.substring(5,12);


Output

shopping


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Hands-On!

Program substringdemo.java will illustrate the

use ofsubstring() method.


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Activity 6.5.1

1. Consider the string declared using the

statement given:

String line = "The sky is blue in color";

Which of the following will convert the string

to lowercase:

a. String a = line.toLowerCase();

b. String b = toLowerCase(line);


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Activity 6.5.1

2. Examine the following code:

String s1 = "Wild";

String s2 = "Flower";

String s3 = "Rose";

String Result;


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Activity 6.5.1

Which of the following statements can be

used to store the string Wild Flower Rosein

Result?

Result = s1.concat( s2.concat( s3 ) );

Result.concat(s1,s2,s3);


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Lab Exercise

1. Write a program to declare a string of your

own and find its length.

2. Write a program to replace a character by agiven character in your string.


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Summary

In this session, you learnt the following:

A string is a sequence of characters.

In Java, string is considered as a class.

Objects of string class will be of string data

type.

Once you create string object you cannotchange the characters that comprise the

string.


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Summary

In this session, you learnt the following:

You can create a string instance using a

string literal. For each string literal, Javaautomatically constructs a string object.

The string class has several methods that

can be used to manipulate the string values.

There are methods to compare two strings,

search for a substring, concatenate two

strings and change the case of letters within

a string.

A i t


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Assignment

1. What is a string?

2. List any three methods in the String class.

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Topic 3 String Part I

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