代做Java Lab 2代做留学生Java程序

日期：2025-02-22 06:48

Java Lab 2

Due: Friday, September 1, 11:00 AM EDT

In this lab, you will practice with a few of the String and StringBuilder methods.

1. Create a project named Lab2. Download the file StringStuff.java from Canvas and copy it to the src directory.

2.  Run the program; enter "gopher" when prompted for a string. What do the boolean values tell you?

3. Create a new String variable s3 and set it equal to the phrase "The name of my pet ". Then:

- display s3

- display s3 in all upper case

- display s3 again: has it changed? Why or why not?

- set s2 to s3 concatenated to " " and to s1 (that is, s3 first) and display it

- concatenate the string " is Fluffy Face" (notice the extra leading space) to s2. Display it.

- display s2 in all lower case.

- display s2 with all "e" characters replaced by "XYZ". Display s2 again – has it changed?

4. Create a new String variable s4 and set it equal to "Barrett,Sales,#44132,8/22/2018". Then:

- display s4

- create an array of strings named slist (like this: String[] slist) and set it equal to the result of splitting s4 on the comma character. Then display slist with this code:

for (String str: slist) {

System.out.println(str);

}

How many lines were printed?

- create a new String[] date and set it equal to slist[3] split on the "/" character. Display the parts of date with similar code to the above loop.

- create a new String s5 and set it equal to the parts of slist concatenated together – the parts are accessed by slist[0], slist[1], etc. Display s5.

5. This problem tests the relative performance of String concatenation versus StringBuilder appending. Use this code to time 10,000 String concatenations:

long startTime = System.currentTimeMillis();

for (int i = 0; i<10000; i++) { s1 += s2; }

long endTime = System.currentTimeMillis();

System.out.println(endTime-startTime);

This will show the number of milliseconds it takes to do the concatenations. Note the use of the long integer type here; it's required by the timer. Comment out the prompt for entering a string and the scanner.next( ) line so it won't annoy you. Run the program.

Create a new StringBuilder object sb with s1 as a parameter. The copy the lines above and paste them back in below the StringBuilder; remove the keyword long (because you've already declared those variables); replace the concatenation of s2 to s1 with appending s2 to the StringBuilder object like this:

sb.append(s2);

Run the program and compare the times.