Question

Language: Java
Create a TryIt.java program with a main method. You are going to use this
program to demonstrate some things about how Java works. Make your methods
here private, because they are not intended to be called from outside the program.
For each test below, make sure that you print to the console:
1) What is being tested
2) The desired output
3) The actual output
Question to be answered: Should you use == or the String method equals
to determine if two Strings are the same?
A. In main, create three Strings using the following pattern:
String varName = “string literal”;
Two of the Strings should be identical.
1) test to see if == works for identical and non-identical String literals.
2
2) test to see if equals works for identical and non-identical String literals
B. Also in main, create three Strings using the following pattern:
String varName = new String(“phrase”);
Use the same phrases you used in part 1. Just create the Strings differently.
Two of the Strings should be identical.
1) test to see if == works for identical and non-identical String literals.
2) test to see if equals works for identical and non-identical String literals
Question to be answered: If you pass an array ( or any other object), and
you change the values of the elements (or the instance variables) in the
method it was passed to, are the values changed back in the calling
method?
C. Create a static method static void testTempVars(). Create this local
variable in the method.
int [] myArray = {3, 4, 5};
Print out the original values using a for loop that makes i go from 0 to 2.
The print statement inside the loop will be:
System.out.println(myArray[i]);
Be sure to label the output as “original values”. Call the testTempVars
method from main.
D. Create another method static void arrayPassing(int []theArray) that
takes an integer array as a parameter. Add 1 to each element of the array
inside the arrayPassing method using a for loop. Print out the array. Be
sure to label the output as “arrayPassing values”.
E. In testTempVars after the print of the original values, call the arrayPassing
method and pass in myArray. Also, at the end of testTempVars, print out all
values in the array again. Be sure to label the output as “values of original
array after arrayPassing executes”.
Question to be answered: If you pass a primitive, and you change the
value of the primitive in the method it was passed to, is the value changed
back in the calling method?
F. In testTempVars add an int variable and initialize it to 10. Print the
variable with an appropriate label indicating this is the original value.
3
G. Create another static void method called primitivePassing that takes an int
parameter. In that method, subtract 5 from the parameter and then print its
value with the label “primitivePassing value”.
H. In testTempVars after the print of the int variable, call the
primitivePassing method and pass in the int variable. After the method
call, print the value of the int variable again. Be sure to label the output as
“values of original array after primitivePassing executes”.

Answer 1

Theory:

String:

String is a collections of charaters. It is a data type in Java which allow variables to store multiple characters.

String Comparison:

For compare two strings we use following methods:

1. using '==' operator:

It compares references not values thats why when we create same values strings using constructor and campare using '==' operator then it return false because both strings reffer different memory location.

2. equals() method:

In this method it compare actual values of strings.

Solution:

Code:

TryIt.java

import java.io.*;
import java.util.*;
class TryIt
{
   private static void testTempVars()
   {
       //creating variable var and initialize to 10
       int var=10;
       //creating Array
       int [] myArray = {3, 4, 5};
       System.out.println("C. Original values");
       //printing array
       for(int i=0;i<3;i++)
       {
           System.out.println(myArray[i]);
       }
       //calling arrayPassing() and pass myArray
       arrayPassing(myArray);
       //original Array
       System.out.println("\nE. values of original array after arrayPassing executes");
       //printing array
       for(int i=0;i<3;i++)
       {
           System.out.println(myArray[i]);
       }
       System.out.println("\nF. original value of var variable="+var);
       //call primitivePassing() function and pass var variable
       primitivePassing(var);
       //print original value of variable
       System.out.println("\nH. values of original variable after primitivePassing executes="+var);

   }
   static void arrayPassing(int []theArray)
   {
       //add 1 in each element of array
       for(int i=0;i<theArray.length;i++)
       {
           theArray[i]=theArray[i]+1;
       }
       System.out.println("\n"+"D. arrayPassing values");
       //printing array
       for(int i=0;i<3;i++)
       {
           System.out.println(theArray[i]);
       }
   }

//for substract 5 from the variable
   static void primitivePassing(int var)
   {
       var=var-5;
       System.out.println("\nG. primitivePassing value="+var);
   }
   public static void main(String[] args) {
       //create string using direct assignments
       String str1="South Africa";
       String str2="America";
       String str3="South Africa";
       //compare strings with '=='
       System.out.println("A.1 Testing strings "+str1+" and "+str2+" by == :");
       System.out.println(str1==str2);
       System.out.println(" Testing strings "+str1+" and "+str3+" by == :");
       System.out.println(str1==str3);
       //compare strings with 'equals()' method
       System.out.println("A.2 Testing strings "+str1+" and "+str2+" by equals :");
       System.out.println(str1.equals(str2));
       System.out.println(" Testing strings "+str1+" and "+str3+" by equals :");
       System.out.println(str1.equals(str3)+"\n");
       //create strings using string constructor
       String var1 = new String("South Africa");
       String var2 = new String("America");
       String var3 = new String("South Africa");
       //compare strings with '=='
       System.out.println("B.1 Testing strings "+var1+" and "+var2+" by == :");
       System.out.println(var1==var2);
       System.out.println(" Testing strings "+var1+" and "+var3+" by == :");
       System.out.println(var1==var3);
       //compare strings with 'equals()' method
       System.out.println("B.2 Testing strings "+var1+" and "+var2+" by equals :");
       System.out.println(var1.equals(var2));
       System.out.println(" Testing strings "+var1+" and "+var3+" by equals :");
       System.out.println(var1.equals(var3)+"\n");
       //calling testTempVars() function
       testTempVars();
   }
}

Output: