You already know by now that Strings in Java are immutable. This means we can’t modify them once created. Hence any changes to them would create a new object in the memory.<\/p>\n
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We would cover the following:<\/p>\n
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However, Java provides the StringBuilder and StringBuffer classes to handle this problem. So with this classes, you can create a string that you can modify.<\/p>\n
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What then is the difference between the two?<\/strong><\/p>\n Note the following differences:<\/p>\n <\/p>\n <\/p>\n <\/p>\n You do this by using the new keyword and calling the StringBuilder constructor. Then you provide a new string. The code below illustrates this<\/p>\n <\/p>\n Listing 1.0: StringBuilder and StringBuffer<\/p>\n <\/p>\n Code in Listing 1.0 creates a StringBuilder string. The next line then appends additional string to the end of the string. We do the same for the StringBuffer<\/p>\n You can see that StringBuilder and StringBuffer are exactly the same in terms of syntax. So based on this, we are just going to focus on StringBuffer.<\/p>\n <\/p>\n <\/p>\n We have a number of useful method provided by the StringBuilder class. You probably should take some time to master some of these methods.<\/p>\n They are listed in Table 1.0 below.<\/p>\n <\/p>\n Table 1.0: StringBuilder Methods<\/p>\n <\/p>\n <\/p>\n 4. Some Examples\u00a0<\/strong><\/p>\n Let’s now demonstrate how some of these methods work. Take a look at the program below. I recommend you make sure to try it yourself. Also look at the comments to see exactly what is happening.<\/p>\n Already you know about the append method. So we\u00a0 examine other methods.<\/p>\n <\/p>\n Listing 1.1: Demonstrating the StringBuilder Methods<\/p>\n <\/p>\n I have added comments to clarify the code. So if you run this code, you will get the output given below.<\/p>\n <\/p>\n <\/p>\n Output of Listing 1.1 Program<\/p>\n <\/p>\n <\/p>\n I then provide a list of other methods in the StringBuilder class. So try to play around with them. In this way you can get your head around them. And it becomes\u00a0 clearer to you as well.<\/p>\n Also note that most of these methods apply also to the String class.<\/p>\n <\/p>\n Returns the current capacity of the String buffer.<\/td>\n<\/tr>\n The given character of the string currently represented by the string buffer, as specified by the index argument, is returned. Returns an int.<\/td>\n<\/tr>\n Sets the the capacity of the buffer is at least equal to the specified value.<\/td>\n<\/tr>\n Characters are copied from this string buffer into the destination given by the char array dst.<\/td>\n<\/tr>\n Returns the particular index within the calling string of the first occurrence of the given substring str.<\/td>\n<\/tr>\n Returns the index within the calling string of the first occurrence of the given substring str, starting at the specified index.<\/td>\n<\/tr>\n Returns the index within the calling string of the rightmost occurrence of the given substring str.<\/td>\n<\/tr>\n Returns the index within the calling string of the last occurrence of the given substring str.<\/td>\n<\/tr>\n Returns the lengthof this StringBuilder. That is number of characters<\/td>\n<\/tr>\n Sets the specified index of this string builder is set to ch.<\/td>\n<\/tr>\n Sets the length of this StringBuilder.<\/td>\n<\/tr>\n Returns a new character sequence that is a subsequence of this calling string.<\/td>\n<\/tr>\n Returns a new String that contains a subsequence of characters currently contained in this StringBuilder. The substring begins at the specified index and extends to the end of the StringBulder.<\/td>\n<\/tr>\n Returns a new String that contains a subsequence of characters currently contained in this StringBuilder.<\/td>\n<\/tr>\n Converts to a string representing the data in the calling StringBuilder.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n Table 1.1: List of other StringBuilder Methods<\/p>\n <\/p>\n\n
2. How then do you create a StringBuilder Object?<\/strong><\/h4>\n
public<\/span> class<\/span> StringBuilderTest<\/span> {<\/span>\r\n\r\n\tpublic<\/span> static<\/span> void<\/span> main<\/span>(<\/span>String[]<\/span> args)<\/span> {<\/span>\r\n\t\t\/\/Creating a StringBuilder object<\/span>\r\n\t\tStringBuilder sbd =<\/span> new<\/span> StringBuilder(<\/span>\"Java\"<\/span>);<\/span>\r\n\t\tsbd.<\/span>append<\/span>(<\/span>\" Tutorials \"<\/span>);<\/span>\r\n\t\t\r\n\t\t\/\/Creating a StringBuffer object<\/span>\r\n\t\tStringBuffer sbf =<\/span> new<\/span> StringBuffer(<\/span>\"Java\"<\/span>);<\/span>\r\n\t\tsbf.<\/span>append<\/span>(<\/span>\" Tutorials\"<\/span>);<\/span>\r\n\t\t\r\n\t\tSystem.<\/span>out<\/span>.<\/span>println<\/span>(<\/span>sbd);<\/span>\r\n\t\tSystem.<\/span>out<\/span>.<\/span>println<\/span>(<\/span>sbf);<\/span>\r\n\t}<\/span>\r\n}<\/span>\r\n<\/pre>\n3. Methods of StringBuilder Class<\/strong><\/h4>\n
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\n SN<\/th>\n Methods and brief description<\/th>\n<\/tr>\n \n 1<\/td>\n append(String s)<\/strong>Modifies a string by appending a new string to the end. Takes boolean, char, int, long, Strings etc as parameter. It returns the modified StringBuffer object.<\/td>\n<\/tr>\n \n 2<\/td>\n reverse()<\/strong>Reverses the value of the given StringBuffer object. For example, abcd becomes dcba. It then returns the modified object.<\/td>\n<\/tr>\n \n 3<\/td>\n delete(int start, int end)<\/strong>Deletes a string from the given StringBuilder object starting from the start index to the end index.<\/td>\n<\/tr>\n \n 4<\/td>\n insert(int offset, int i)<\/strong>Inserts a string\u00a0s<\/b>\u00a0into\u00a0 the position specified by the offset.<\/td>\n<\/tr>\n \n 5<\/td>\n replace(int start, int end, String str)<\/strong>Replaces the characters in the substring of the StringBuilder with characters in the given String.<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n public<\/span> class<\/span> StringBuilderTest<\/span> {<\/span>\r\n\r\n\tpublic<\/span> static<\/span> void<\/span> main<\/span>(<\/span>String[]<\/span> args)<\/span> {<\/span>\r\n\t\tStringBuilder sbd =<\/span> new<\/span> StringBuilder(<\/span>\"Java\"<\/span>);<\/span>\r\n\t\t\r\n\t\t\/\/1. The append method<\/span>\r\n\t\tsbd.<\/span>append<\/span>(<\/span>\" Tutorials \"<\/span>);<\/span>\r\n\t\tSystem.<\/span>out<\/span>.<\/span>println<\/span>(<\/span>\"1. : \"<\/span> +<\/span> sbd);<\/span>\r\n\t\t\r\n\t\t\/\/2. The reverse method<\/span>\r\n\t\tsbd.<\/span>reverse<\/span>();<\/span>\r\n\t\tSystem.<\/span>out<\/span>.<\/span>println<\/span>(<\/span>\"2. :\"<\/span> +<\/span> sbd);<\/span>\r\n\t\t\r\n\t\t\/\/3. Reverse it back to normal<\/span>\r\n\t\tsbd.<\/span>reverse<\/span>();<\/span>\r\n\t\tSystem.<\/span>out<\/span>.<\/span>println<\/span>(<\/span>\"3. : \"<\/span> +<\/span> sbd);<\/span>\r\n\r\n\t\t\/\/4. Deletes the first 4 characters<\/span>\r\n\t\tsbd.<\/span>delete<\/span>(<\/span>0<\/span>,<\/span> 4<\/span>);<\/span>\r\n\t\tSystem.<\/span>out<\/span>.<\/span>println<\/span>(<\/span>\"4. :\"<\/span> +<\/span> sbd);<\/span>\r\n\t\t\r\n\t\t\/\/5. Insert JavaScript in the first index of 0<\/span>\r\n\t\tsbd.<\/span>insert<\/span>(<\/span>0<\/span>,<\/span> \"JavaScript\"<\/span>);<\/span>\r\n\t\tSystem.<\/span>out<\/span>.<\/span>println<\/span>(<\/span>\"5. : \"<\/span> +<\/span> sbd);<\/span>\r\n\t\t\r\n\t\t\/\/6. Replace JavaScript with AngularJs<\/span>\r\n\t\tsbd.<\/span>replace<\/span>(<\/span>0<\/span>,<\/span> 10<\/span>,<\/span> \"AngularJS\"<\/span>);<\/span>\r\n\t\tSystem.<\/span>out<\/span>.<\/span>println<\/span>(<\/span>\"6. : \"<\/span> +<\/span> sbd);<\/span>\r\n\t}<\/span>\r\n}<\/span>\r\n<\/pre>\n1<\/span>.<\/span> :<\/span> Java Tutorials \r\n2<\/span>.<\/span> :<\/span> slairotuT avaJ\r\n3<\/span>.<\/span> :<\/span> Java Tutorials \r\n4<\/span>.<\/span> :<\/span> Tutorials \r\n5<\/span>.<\/span> :<\/span> JavaScript Tutorials \r\n6<\/span>.<\/span> :<\/span> AngularJS Tutorials \r\n<\/pre>\n5. Other StringBuilder Methods<\/strong><\/h4>\n
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\n SN<\/th>\n Method and description<\/th>\n<\/tr>\n \n 1<\/td>\n capacity()<\/b><\/p>\n \n 2<\/td>\n charAt(int index)<\/b><\/p>\n \n 3<\/td>\n void ensureCapacity(int minimumCapacity)<\/b><\/p>\n \n 4<\/td>\n void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)<\/b><\/p>\n \n 5<\/td>\n indexOf(String str)<\/b><\/p>\n \n 6<\/td>\n int indexOf(String str, int fromIndex)<\/b><\/p>\n \n 7<\/td>\n int lastIndexOf(String str)<\/b><\/p>\n \n 8<\/td>\n int lastIndexOf(String str, int fromIndex)<\/b><\/p>\n \n 9<\/td>\n int length()<\/b><\/p>\n \n 10<\/td>\n void setCharAt(int index, char ch)<\/b><\/p>\n \n 11<\/td>\n void setLength(int newLength)<\/b><\/p>\n \n 12<\/td>\n CharSequence subSequence(int start, int end)<\/b><\/p>\n \n 13<\/td>\n String substring(int start)<\/b><\/p>\n \n 14<\/td>\n String substring(int start, int end)<\/b><\/p>\n \n 15<\/td>\n String toString()<\/b><\/p>\n Watch the Video<\/strong><\/a><\/h4>\n