THE CONCEPT CLASSES
...initiated by DEYS
IIT- JEE Pre for Classes VII ~ X (ICSE)
Java String Manual
String Constructor
1)
String s;
// s is declared as a variable of String class, but object not created.
s = “ABC”;
// objected created and initialized
2)
String s = new String();
3)
String s1= “ABC”, s2= new String();
4)
String s = new String(“ABC”);
5)
String s1 = “abcxyz”;
String s2 = new String(s1);
= > s2 =”abcxyz”;
common error
String s = new String(„a‟);
// Error
String Concatenation
1)
String s = “abc”+”xyz”;
= > s = “abcxyz”
2)
String s1 = “abc”;
String s = s1+“xyz”;
= > s = ”abcxyz”
3)
String s = “abc”+2+2;
= > s = “abc22”;
4)
String s = “abc”+(2+2);
= > s = “abc4”
5)
String s1 = “One”; String s2 = “Ten”;
s2=s1.concat(s2);
= > s2 = “OneTen”
6)
String s = new String( ) ;
s = s + “abc”;
// No Error as object s has already created and stores null value.
CONCEPT
common error
String s;
s = s + “abc”
// No object has been created for s
// Error
charAt()
->char charAt(int index)
String s = “abc”;
char c= s.charAt(0);
String Comparison
1)
equals()
=> c = ‟a‟
-> boolean equals(String)
2)
euualsIgnoreCase() -> boolean equals(String)
String s1 = “abc”, s2 = “AbC”;
s1.equals(s2)
= > false
s2.equalsIgnoreCase(s1)
= > true
3)
startsWith() / endsWith()
- > boolean startsWith(String s)
- > boolean startsWith(String s, int startIndex)
- > boolean endsWith(String s)
String s = “The Concept Classes …initiated by DEYS”;
s.startsWith(“The Con”)
= > true
s.startsWith(“the”)
= > false
s.startsWith(“Concept”,4)
s.endsWith(“DEYS”)
4)
equals()
// Compares characters
String s1 =”abc”;
String s2 = new String(s1);
String s3 =”ABC”;
String s4 =s1;
s1.equals(s2)
s1.equals(s3)
s1.equals(s4)
s1 = = s4
s1 = = s2
= > true
= > true
==
// Compares object references
CONCEPT
= > true
= > false
= > true
= > true
= > false
//Compares characters
//Compares characters
//Compares characters
//Compares object reference
//Compares object reference
5)
compareTo() - > int compareTo(string s)
String s1 = “ABC” , s2 =”ABCxyz” , s3 =”ABCxyz7”;
String s4 =”ABcxyz7” , s5 =”Adgaf”;
s1.compareTo(s2)
= > -3 // Difference in number of characters
s1.compareTo(s3)
= > - 4 // Difference in number of characters
s2.compareTo(s1)
= > 3 // Difference in number of characters
s1.compareTo(s4)
= > -32 // Difference in UNICODE of characters of 1st diff.
s4.compareTo(s1)
= > 32 // Difference in UNICODE of characters of 1st diff.
s4.compareTo(s5)
= > -34 // Difference in UNICODE of characters of 1st diff.
s1.compareTo(s1)
= > 0 // Difference in UNICODE of characters of 1st diff.
6)
compareToIgnoreCase()
- > int compareToIgnoreCase(String s)
Completely same as compareTo() only ignores any change in case.
7)
indexOf()
-> int indexOf( int ch)
// if ch is char implicit type casting will take place to int
-> int indexOf( String str)
// searches the first occurrence of the str
-> int indexOf( int ch, int startIndex)
-> int indexOf(String str, int startIndex)
String s=”The Concept Classes …initiated by DEYS”;
s.indexOf(„e‟)
= >2
s.indexOf(67)
= >4
s.indexOf(„e‟,4)
= >8
s.indexOf(“once”)
= >5
s.indexOf(“once”,4)
= >5
s.indexOf(“once”,6)
= >-1
// if search fails -1 is returned
s.indexOf(“once”,5)
= >5
s.indexOf(“Once”)
= >-1
8)
lastIndexOf()
-> int lastIndexOf( int ch)
// if ch is char implicit type casting will take place to int
-> int lastIndexOf( String str) // searches the last occurrence of the str
-> int lastIndexOf( int ch, int startIndex)
-> int lastIndexOf(String str, int startIndex)
String s=”The Concept Classes …initiated by DEYS”;
s.lastIndexOf(„C‟)
= >12
s.lastIndexOf(67,5)
= >4
s.lastIndexOf(„o‟,4)
= >-1 // if search fails -1 is returned
s.lastIndexOf(“once”)
= >5
s.lastIndexOf(“once”,3)
= >-1
s.lastIndexOf(“once”,5)
= >5
Modifying Strings
1)
substring()
-> String substring(int startIndex)
// Note : s for string in substring is small
-> String substring(int startIndex, int endIndex)
String s = “Delhi is the capital of India”;
s.substring(2)
= >”lhi is the capital of India”
s.substring(6,10)
= >”is t” // endIndex is not included
2)
replace()
- > String replace(char old, char new)
String s1 = “Java is platform independent language”;
String s2 = s1.replace(„a‟,‟e‟);
= > s2 = “Jeve is pletform independent lenguege”
3)
length()
-> int length()
String s =”India and Asia”;
int len = s.length()
4)
trim()
-> String trim()
String s =” India “;
int len = s.length();
s=s.trim();
len = s.length();
= > len = 14
=> len = 11
= > s = “India”
=> len = 5
5)
toUpperCase() / toLowerCase()
- > String toUpperCase()
- > String toLowerCase()
String s = “aVg+e-H*g/5! #$%^&*()”;
String s1 =s.toUpperCase();
=> s1= AVG+E-H*G/5! #$%^&*()”
String s2 =s.toLowerCase();
=> s2 = “avg+e-h*g/5! #$%^&*()”
6)
valueOf() Vs toString()
valueOf( ) is a static method of String class which can be used to converts primitive data type to
string.
toString( ) are static methods of all wrapper classes that can be used to converts primitive data type
to string.
-> String valueOf(anyPrimitiveLiteral/Variable)
-> String toString(correspondingPrimitiveLiteral/Variable)
int x =89;
String s1 = String.valueOf(x);
= > s1 = “89”
String s2 = String.valueOf(123);
= > s2 = “123”
String s3 = Integer.toString(x);
= > s3 = “89”
String s1 = Integer.toString(123);
= > s4 = “123”
Every object implements toString( ) method. It is a method which returns a string of the object.
class Test
{
int x,y,z;
Test (int a, int b)
{
x=a;
y=b;
}
void cal()
{
z=x+y;
}
CONCEPT
public String toString()
{
return ” Sum of “ + x +” and “ + y + “ is “ + z;
}
}
CONCEPT
class TestToString
{
public static void main(String arg[])
{
Test t1 = new Test(3,4);
t1.cal( );
Test t2 = new Test(7,8);
t2.cal( );
String s = “”+ t2;
//*
System.out.println(t1);
System.out.println(s);
}
}
Output:
Sum of 3 and 4 is 7
Sum of 7 and 8 is 15
* Note: Directly t2 can‟t be assigned to String s as it will give reference to String object which
does not match on type.
IIT JEE Selections
2014
Harsh Sahu
Ashish Singh
IIT Delhi – Mechanical
IIT Dhanbad – Mining
Kapil Singh
Aadil Hayat
Pallavi Sahu
IIT Roorkee – Computer Science
IIT K – Aero Space
IIT Roorkee – Geo Physics
Gautam Pratap Singh (Jhansi Topper)
Gurjyot Singh Sethi
IIT K - Mechanical
IIT K - Civil
Vaibhav Agarwal (Jhansi Topper)
Himanshu Sahu
Ayush Nigam
IIT D – Mechanical
IIT Raj – Mechanical
ISM Dhanbad – Petro Chemical
2013
2012
2011
IIT JEE Pre for classes VII ~ X
Physics, Chemistry, Mathematics, Biology & Computer
Address : The Concept Classes …initiated by DEYS, Near Ashik Chauraha, Basement Archana Kirana
Store, Antia Tal Road, Jhansi.
Mr. A.K. DEY(MCA)
Mob: 9451520537