How do you use compareto method?

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public class AboutStrings{ public static void main(String args[]){ String s1="hello"; String s2="hel"; String s3="lo"; String s4=s2+s3; //to know the hash codes of s1,s4. System.out.println(s1.hashCode()); System.out.println(s4.hashCode()); // these two s1 and s4 are having same hashcodes. if(s1==s4){ System.out.println("s1 and s4 are same."); }else System.out.println("s1 and s4 are not same."); } } Somebody told me that, == operator compares references of the objects. In the above example even though s1 and s4 are refering to same object(having same hash codes), it is printing s1 and s4 are not same. Can anybody explain in detail why it is behaving like this? Thanks in Advance RavuriVinod

4 Answers   TCS,

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what is meta-Inf?

2 Answers   Polaris,

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What is java beans?

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Can we declare a static variable inside a method?

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Distinguish between a predicate and a function?

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What are local variables?

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The following program reads data (details of students) from a file named students.txt and converts it into e-mail addresses. The results are written to a file named studentemail.txt. students.txt consists of a number of lines, each containing the data of a student in colon delimited format: Last Name:First Name:Student Number Each input record is converted to an e-mail address and written to studentemail.txt in the following format: the first character of the last name + the first character of the first name + the last four digits of the student number + “@myunisa.ac.za” import java.io.*; public class EmailConverter { public static void main(String[] args) throws IOException { BufferedReader input = new BufferedReader(new FileReader ("students.txt")); PrintWriter output = new PrintWriter(new FileWriter ("studentemail.txt")); String line = input.readLine(); while (line != null) { // Extract the information for each student String[] items = line.split(":"); // Generate the email address String email = "" + items[0].charAt(0) + items[1].charAt(0) + items[2].substring(4,8) + "@myunisa.ac.za"; email = email.toLowerCase(); // Output output.println(email); line = input.readLine(); } input.close(); output.close(); } } Rewrite the class so that it handles possible errors that may occur. In particular, it should do the following: • It should catch at least three appropriate exceptions that might occur, and display suitable messages. • At this stage, the program will not run correctly if there is an empty line in the input file. Change the program so that if an empty line is encountered, an exception is thrown and the empty line is ignored. This exception should be handled with the display of a suitable error message. • Before the e-mail address is added to the output file, check if the student number has 8 digits. If not, throw an InvalidFormatException (which the program should not handle itself)

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What is exception handling in java?

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How does hashmap work in java ?

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Does java list allow null?

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What is the difference between choice and list?

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