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In java, string concatenation forms a new string that is the combination of multiple strings. There are two ways to concat string in java:
Java string concatenation operator (+) is used to add strings. For Example:
The Java compiler transforms above code to this:
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:
The String concat() method concatenates the specified string to the end of current string. Syntax:
Let's see the example of String concat() method.
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:
The String equals() method compares the original content of the string. It compares values of string for equality. String class provides two methods:
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:
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.
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:
In such case, s points to the "Sachin Tendulkar". Please notice that still sachin object is not modified.
|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.|
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.
str : another string i.e. compared with this string.
It returns true if characters of both strings are equal ignoring case otherwise false.
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.
anotherObject : another object i.e. compared with this string.
true if characters of both strings are equal otherwise false.
equals() method of java Object class.
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.
The syntax or signature of endsWith() method is given below.
suffix : Sequence of character
true or false
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.
The signature of string contains() method is given below:
sequence : specifies the sequence of characters to be searched.
true if sequence of char value exists, otherwise false.
NullPointerException : if sequence is null.
The java string concat() method combines specified string at the end of this string. It returns combined string. It is like appending another string.
The signature of string concat() method is given below:
anotherString : another string i.e. to be combined at the end of this string.
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.
anotherString: represents string that is to be compared with current string
an integer value
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.
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.
The signature of string charAt() method is given below:
index : index number, starts with 0
StringIndexOutOfBoundsException : if index is negative value or greater than this string length.
Let's see the example of charAt() method where we are passing greater index value. In such case, it throws StringIndexOutOfBoundsException at run time.