What is difference and similarities between concat() and append() in java,given reason and example?

Question

Given two strings, append them together (known as "concatenation") and return the result. However, if the concatenation creates a double-char, then omit one of the chars. If the inputs are "Mark" and "Kate" then the output should be "markate". (The output should be in lowercase).

Answer 1

String concat() method concatenate or join two strings like String s1 and String s2 and return a third string(s3) as a result.
String s1="Uttar";
String s2="Pradesh";
String s3=s1.concat(s2);
String concat() method is immutable methods. In this method content of sting variable are not modify.
But append() method is mutable method of StingBuffer class. in this method content of StringBuffer class variable are modify.
StringBuffer sb=new StringBuffer("Uni");
sb.append("versity");
Preceding statements produce:"University".