Study Anytime Any Where We Will Open The Knowledge For You Anish Sir 24x7 Learning solution It Is Time to join JOB
25 May 2018

Study Anytime Any Where

25 May 2018

We Will Open The Knowledge For You

25 May 2018

Anish Sir 24x7 Learning solution

25 May 2018

It Is Time to join JOB

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Anish Sir

Anish Sir

"I am delighted once again to pen the welcome note to the Tosh!Yas Technologies ."

 Call +91 74 88 34 7779  | Email : anishsingh@live.com

Website URL: http://toshiyas.in
Monday, 24 July 2017 04:09

String Concatenation in Java

In java, string concatenation forms a new string that is the combination of multiple strings. There are two ways to concat string in java:

  1. By + (string concatenation) operator
  2. By concat() method

1) String Concatenation by + (string concatenation) operator

Java string concatenation operator (+) is used to add strings. For Example:

 
  1. class TestStringConcatenation1{  
  2.  public static void main(String args[]){  
  3.    String s="Sachin"+" Tendulkar";  
  4.    System.out.println(s);//Sachin Tendulkar  
  5.  }  
  6. }  
Output:Sachin Tendulkar

The Java compiler transforms above code to this:

 
  1. String s=(new StringBuilder()).append("Sachin").append(" Tendulkar).toString();  

In java, String concatenation is implemented through the StringBuilder (or StringBuffer) class and its append method. String concatenation operator produces a new string by appending the second operand onto the end of the first operand. The string concatenation operator can concat not only string but primitive values also. For Example:

 
  1. class TestStringConcatenation2{  
  2.  public static void main(String args[]){  
  3.    String s=50+30+"Sachin"+40+40;  
  4.    System.out.println(s);//80Sachin4040  
  5.  }  
  6. }  
80Sachin4040

Note: After a string literal, all the + will be treated as string concatenation operator.

2) String Concatenation by concat() method

The String concat() method concatenates the specified string to the end of current string. Syntax:

 
  1. public String concat(String another)  

Let's see the example of String concat() method.

 
  1. class TestStringConcatenation3{  
  2.  public static void main(String args[]){  
  3.    String s1="Sachin ";  
  4.    String s2="Tendulkar";  
  5.    String s3=s1.concat(s2);  
  6.    System.out.println(s3);//Sachin Tendulkar  
  7.   }  
  8. }  
Sachin Tendulkar
Monday, 24 July 2017 04:06

Java String compare

We can compare string in java on the basis of content and reference.

It is used in authentication (by equals() method), sorting (by compareTo() method), reference matching (by == operator) etc.

There are three ways to compare string in java:

  1. By equals() method
  2. By = = operator
  3. By compareTo() method

1) String compare by equals() method

The String equals() method compares the original content of the string. It compares values of string for equality. String class provides two methods:

  • public boolean equals(Object another) compares this string to the specified object.
  • public boolean equalsIgnoreCase(String another) compares this String to another string, ignoring case.
 
  1. class Teststringcomparison1{  
  2.  public static void main(String args[]){  
  3.    String s1="Sachin";  
  4.    String s2="Sachin";  
  5.    String s3=new String("Sachin");  
  6.    String s4="Saurav";  
  7.    System.out.println(s1.equals(s2));//true  
  8.    System.out.println(s1.equals(s3));//true  
  9.    System.out.println(s1.equals(s4));//false  
  10.  }  
  11. }  
Output:true
       true
       false
 
  1. class Teststringcomparison2{  
  2.  public static void main(String args[]){  
  3.    String s1="Sachin";  
  4.    String s2="SACHIN";  
  5.   
  6.    System.out.println(s1.equals(s2));//false  
  7.    System.out.println(s1.equalsIgnoreCase(s3));//true  
  8.  }  
  9. }  
Output:false
       true
Monday, 24 July 2017 04:04

Immutable String in Java

In java, string objects are immutable. Immutable simply means unmodifiable or unchangeable.

Once string object is created its data or state can't be changed but a new string object is created.

Let's try to understand the immutability concept by the example given below:

 
  1. class Testimmutablestring{  
  2.  public static void main(String args[]){  
  3.    String s="Sachin";  
  4.    s.concat(" Tendulkar");//concat() method appends the string at the end  
  5.    System.out.println(s);//will print Sachin because strings are immutable objects  
  6.  }  
  7. }  

Test it Now

Output:Sachin

Now it can be understood by the diagram given below. Here Sachin is not changed but a new object is created with sachintendulkar. That is why string is known as immutable.

Heap diagram

As you can see in the above figure that two objects are created but s reference variable still refers to "Sachin" not to "Sachin Tendulkar".

But if we explicitely assign it to the reference variable, it will refer to "Sachin Tendulkar" object.For example:

 
  1. class Testimmutablestring1{  
  2.  public static void main(String args[]){  
  3.    String s="Sachin";  
  4.    s=s.concat(" Tendulkar");  
  5.    System.out.println(s);  
  6.  }  
  7. }  

Test it Now

Output:Sachin Tendulkar

In such case, s points to the "Sachin Tendulkar". Please notice that still sachin object is not modified.


Why string objects are immutable in java?

Because java uses the concept of string literal.Suppose there are 5 reference variables,all referes to one object "sachin".If one reference variable changes the value of the object, it will be affected to all the reference variables. That is why string objects are immutable in java.
Monday, 24 July 2017 04:03

Java String equalsIgnoreCase()

The String equalsIgnoreCase() method compares the two given strings on the basis of content of the string irrespective of case of the string. It is like equals() method but doesn't check case. If any character is not matched, it returns false otherwise it returns true.


Signature

 
  1. public boolean equalsIgnoreCase(String str)  

Parameter

str : another string i.e. compared with this string.


Returns

It returns true if characters of both strings are equal ignoring case otherwise false.


Java String equalsIgnoreCase() method example

 
  1. public class EqualsIgnoreCaseExample{  
  2. public static void main(String args[]){  
  3. String s1="javatpoint";  
  4. String s2="javatpoint";  
  5. String s3="JAVATPOINT";  
  6. String s4="python";  
  7. System.out.println(s1.equalsIgnoreCase(s2));//true because content and case both are same  
  8. System.out.println(s1.equalsIgnoreCase(s3));//true because case is ignored  
  9. System.out.println(s1.equalsIgnoreCase(s4));//false because content is not same  
  10. }}  
true
true
false
Monday, 24 July 2017 04:00

Java String equals

The java string equals() method compares the two given strings based on the content of the string. If any character is not matched, it returns false. If all characters are matched, it returns true.

The String equals() method overrides the equals() method of Object class.


Signature

 
  1. public boolean equals(Object anotherObject)  

Parameter

anotherObject : another object i.e. compared with this string.


Returns

true if characters of both strings are equal otherwise false.


Overrides

equals() method of java Object class.


Java String equals() method example

 
  1. public class EqualsExample{  
  2. public static void main(String args[]){  
  3. String s1="javatpoint";  
  4. String s2="javatpoint";  
  5. String s3="JAVATPOINT";  
  6. String s4="python";  
  7. System.out.println(s1.equals(s2));//true because content and case is same  
  8. System.out.println(s1.equals(s3));//false because case is not same  
  9. System.out.println(s1.equals(s4));//false because content is not same  
  10. }}  
true
false
false
Monday, 24 July 2017 03:58

Java String endsWith

The java string endsWith() method checks if this string ends with given suffix. It returns true if this string ends with given suffix else returns false.


Signature

The syntax or signature of endsWith() method is given below.

 
  1. public boolean endsWith(String suffix)  

Parameter

suffix : Sequence of character


Returns

true or false


Java String endsWith() method example

 
  1. public class EndsWithExample{  
  2. public static void main(String args[]){  
  3. String s1="java by javatpoint";  
  4. System.out.println(s1.endsWith("t"));  
  5. System.out.println(s1.endsWith("point"));  
  6. }}  

Output:

true
true
Monday, 24 July 2017 03:57

Java String contains

The java string contains() method searches the sequence of characters in this string. It returns true if sequence of char values are found in this string otherwise returns false.


Signature

The signature of string contains() method is given below:

 
  1. public boolean contains(CharSequence sequence)  

Parameter

sequence : specifies the sequence of characters to be searched.


Returns

true if sequence of char value exists, otherwise false.


Throws

NullPointerException : if sequence is null.


Java String contains() method example

 
  1. class ContainsExample{  
  2. public static void main(String args[]){  
  3. String name="what do you know about me";  
  4. System.out.println(name.contains("do you know"));  
  5. System.out.println(name.contains("about"));  
  6. System.out.println(name.contains("hello"));  
  7. }}  
true
true
false
Monday, 24 July 2017 03:56

Java String concat

The java string concat() method combines specified string at the end of this string. It returns combined string. It is like appending another string.


Signature

The signature of string concat() method is given below:

 
  1. public String concat(String anotherString)  

Parameter

anotherString : another string i.e. to be combined at the end of this string.


Returns

combined string


Java String concat() method example

 
  1. public class ConcatExample{  
  2. public static void main(String args[]){  
  3. String s1="java string";  
  4. s1.concat("is immutable");  
  5. System.out.println(s1);  
  6. s1=s1.concat(" is immutable so assign it explicitly");  
  7. System.out.println(s1);  
  8. }}  
  9. java string
    java string is immutable so assign it explicitly
Monday, 24 July 2017 03:54

Java String compareTo()

The java string compareTo() method compares the given string with current string lexicographically. It returns positive number, negative number or 0.

It compares strings on the basis of Unicode value of each character in the strings.

If first string is lexicographically greater than second string, it returns positive number (difference of character value). If first string is less than second string lexicographically, it returns negative number and if first string is lexicographically equal to second string, it returns 0.

 
  1. if s1 > s2, it returns positive number  
  2. if s1 < s2, it returns negative number  
  3. if s1 == s2, it returns 0  

Signature

 
  1. public int compareTo(String anotherString)  

Parameters

anotherString: represents string that is to be compared with current string


Returns

an integer value


Java String compareTo() method example

 
  1. public class CompareToExample{  
  2. public static void main(String args[]){  
  3. String s1="hello";  
  4. String s2="hello";  
  5. String s3="meklo";  
  6. String s4="hemlo";  
  7. String s5="flag";  
  8. System.out.println(s1.compareTo(s2));//0 because both are equal  
  9. System.out.println(s1.compareTo(s3));//-5 because "h" is 5 times lower than "m"  
  10. System.out.println(s1.compareTo(s4));//-1 because "l" is 1 times lower than "m"  
  11. System.out.println(s1.compareTo(s5));//2 because "h" is 2 times greater than "f"  
  12. }}  

Output:

0
-5
-1
2

Java String compareTo(): empty string

If you compare string with blank or empty string, it returns length of the string. If second string is empty, result would be positive. If first string is empty, result would be negative.

 
  1. public class CompareToExample2{  
  2. public static void main(String args[]){  
  3. String s1="hello";  
  4. String s2="";  
  5. String s3="me";  
  6. System.out.println(s1.compareTo(s2));  
  7. System.out.println(s2.compareTo(s3));  
  8. }}  

Output:

5
-2
Monday, 24 July 2017 03:53

Java String charAt()

The java string charAt() method returns a char value at the given index number. The index number starts from 0. It returns StringIndexOutOfBoundsException if given index number is greater than this string or negative index number.


Signature

The signature of string charAt() method is given below:

 
  1. public char charAt(int index)  

Parameter

index : index number, starts with 0


Returns

char value


Specified by

CharSequence interface


Throws

StringIndexOutOfBoundsException : if index is negative value or greater than this string length.


Java String charAt() method example

 
  1. public class CharAtExample{  
  2. public static void main(String args[]){  
  3. String name="javatpoint";  
  4. char ch=name.charAt(4);//returns the char value at the 4th index  
  5. System.out.println(ch);  
  6. }}  

Output:

t

StringIndexOutOfBoundsException with charAt()

Let's see the example of charAt() method where we are passing greater index value. In such case, it throws StringIndexOutOfBoundsException at run time.

 
  1. public class CharAtExample{  
  2. public static void main(String args[]){  
  3. String name="javatpoint";  
  4. char ch=name.charAt(10);//returns the char value at the 10th index  
  5. System.out.println(ch);  
  6. }}  

Output:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: 
String index out of range: 10
at java.lang.String.charAt(String.java:658)
at CharAtExample.main(CharAtExample.java:4)

 

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