Strings

And other things

Strings Overview

The String Class and its methods The char data type and Character class StringBuilder, StringTokenizer classes Printf() method The StringBuffer class

What is a string

A sequence of characters Representing alphanumeric data. Defined in the java.lang.String class String is a class and objects of String type

are reference variables.

Making a string

Declared as a typical object would be. String s= new String(“Hello”)

Or using a short hand that java provides String s = “Hello”

The string class provides many methods. charAt(int idx) compareTo(string s) concat(string s) equals(string s) indexOf(int ch,int fromhere) lastIndexOf(int ch,int fromhere) length() replace(char old, char new) substring(int beginidx, int endidx) trim() toUpper(String s)

Joining strings

Concatenation is the operation of joining one string on the end of another.

S3 = S.concat(S2) Or S3 = S + S2 Java will implicitly type cast a numeric

value as a string

String literals

“Hello” “Good bye” “10,100” “576DSW” “700-6000” “Bill”

String equality

String s1=“Hello” String s2=“Hello”

If (s1==s2) System.out.print(“Equal”) Not equal

If (s1.equals(s2)) System.out.print(“Equal”) Equal

String s3=s1 If (s3==s1) System.out.print(“Equal”)

Equal

String comparisons

If S1 < S2 may not work correctly If (S1.compareTo(s2)) < 0

System.out.print(“Less then”) If (S1.compareTo(s2)) == 0

System.out.print(“Equals”) If (S1.compareTo(s2)) > 0

System.out.print(“Greater then”)

Finding strings in strings

indexOf(int ch,int fromhere) lastIndexOf(int ch,int fromhere) indexOf(String S, int fromhere) S1=“Hello” S1.indexof(‘l’)

Will return 2 S1.lastindexof(‘l’)

Will return 3

String Conversions

String.valueof(number)Returns a string

And Integer.parseint(String)Return a number

Converting Strings

ToLowerCase() ToUppercase()

The stringbuffer class

Like the string class Why 2 string classes? Other methods: .delete(int loc, int toloc) .reverse() .capacity() the size of the stringbuffer

Char data type

A char is a single unicode value Unicode is a code used to specify character

data.

char c; char[] carray = { ‘H’, ‘e’, ‘l’, ‘l’, ‘o’ }; A character array can be used to build a string String s= new String(carray)

Command line arguments

Command line arguments are passed to the args array in the main method.

We can find the length of this array and process these arguments in our program.

That Character class

A wrapper class These are likes like Double and Integer which can be

used in place of the primitive data types. There is one for each primitive data type

Provides methods like: compareTo( char) equals(char) Character.isDigit(char) // a static method Also: isLetter(char) and isLowerCase()…

StringBuilder

An object that can be created to manipulate strings values mutably then store the result back into a string.

Methods: append( String) insert(index, String) deleteCharAT( index) replace( startindex, endindex, string) toString()

StringTokenizer

Used to break strings apart. This process is also known as parsing a string.

A token is a special character used to delimit the parts of a string. nextToken() countTokens()

The default token is set to “ \t\n\r\f” the white space characters.

We can change this using the optional constructor.. StringTokenizer( string, tokenString)

Formatting data

The printf() method of PrintStream class Format specifiers:

%.2f - a double value, 2 decimals %d - an integer %x - hexvalue

System.out.printf(“data = %.2f”, data); Formatting dates:

%tA, %tB, %td, %tY For day, month, dayof month, year

Argument index value

System.out.printf(“%1$d, %2$.2f” , int, double) The 1$ and 2$ are used to specify the index of

the parameter to use. By default the value of 1 is used. Field width: %3d - specifies the integer with room for 3 digits

Justification

%-15s - left justify a string of 15 characters %15s- default right justify the string

The format method Formatter f = new Formatter() F.format( “formatstring”, args…)

Or outstring =String.format( formatstring, args…)

Summary

Strings Characters Char Format and sprint methods Importance of API documentation