COP EXAM 2
Which of the following is the correct expression that evaluates to true if the number x is between 1 and 100 or the number is negative?
( (x < 100) && (x > 1) ) || (x < 0)
Suppose that x is an int variable. Which of the following expressions always evaluates to false?
(x > 0) && ( x <= 0)
break statements:
-A break statement can be used to end a loop immediately. -The break statement ends only the innermost loop or switch statement that contains the break statement. -break statements make loops more difficult to understand. -Use break statements sparingly (if ever). ex: public class TestBreak { public static void main(String[] args) { int sum = 0; int number = 0; while (number < 20) { number++; sum += number; if (sum >= 100) break; } System.out.println("The number is " + number); System.out.println("The sum is " + sum); } }
do-while loop
-A do-while statement repeats while a controlling boolean expression remains true -The loop body typically contains an action that ultimately causes the controlling boolean expression to become false. -A do-while loop can be used to replace a while loop if the loop body has to be executed before testing the continuation condition. 25 ex: //1. initialize control variable int counter = 0; do{ //body of the do/while loop System.out.println ("My birthday is July 21 and counter is: " + counter); //3.Update the control variable's value counter ++; } while ( counter < 20); //2. condtion that involves the control varibale System.out.print("OUTSIDE OF DO-WHILE LOOP!");
for statement
-A for statement executes the body of a loop a fixed number of times - In general, a for loop may be used if the number of repetitions is known, as, for example, when you need to print a message 100 times. format: for (Initialization, Condition, Update) Body_Statement ex: int i; for(i=0;i< 2;i++){ System.out.println("Welcome to Java!"); }
while loop
-A while statement repeats while a controlling boolean expression remains true -The loop body typically contains an action that ultimately causes the controlling boolean expression to become false. -A while loop may be used if the number of repetitions is not known, as in the case of reading the numbers until the input is 0. ex: //1.Initialize control variable int count = 20; //2. Start the while loop while (count < 20) { System.out.println ("My my birthday is November 1!!! and the value of count is: " + count ); //3. Update the value of the control variable count = count + 1; }// end of while loop
purpose of a break statement
-The keyword break is optional, but it should be used at the end of each case in order to terminate the remainder of the switch statement -If the break statement is not present, the next case statement will be executed
formatting output using printf
-Use the printf statement: System.out.printf(format, items); -Where format is a string that may consist of substrings and format specifiers. - A format specifier specifies how an item should be displayed. - An item may be a numeric value, character, boolean value, or a string. - Each specifier begins with a percent sign (%)
Logical operator (important)
-an expression made up of Boolean values and logical operations that evaluates true or false -evaluates left to right
String methods: Simple string methods --> concat(s1)
-returns a new string that concatenates this string with string s1 ex: given --> String fname = "Mary"; String lname = "Smith"; name = fname.concat(lname); gives back: MarySmith
String methods: Simple string methods --> toLowerCase()
-returns a new string with all letters in lowercase ex: given --> String message1 = "Welcome"; message1.toLowerCase(); gives back: welcome
String methods: Simple string methods --> toUpperCase()
-returns a new string with all letters in uppercase ex: given --> String message1 = "Welcome"; message1.toUpperCase(); gives back: WELCOME
String methods: Simple string methods --> trim()
-returns a new string with whitespace characters trimmed on both sides ex: given --> String message2 = " Welcome " message2.trim(); gives back: Welcome (no spaces)
String methods Methods for comparing strings --> compareTo(s1)
-returns an integer greater than 0, equal to 0, or less than 0 to indicate whether the string is greater than, equal to, or less than s1 ex: given --> String s1="hello"; String s2="hello"; String s3="meklo"; String s4="hemlo"; String s5="flag"; System.out.println(s1.compareTo(s2)); //0 because both are equal System.out.println(s1.compareTo(s3)); //-5 because "h" is 5 times lower than "m" System.out.println(s1.compareTo(s4)); //-1 because "l" is 1 times lower than "m" System.out.println(s1.compareTo(s5)); //2 because "h" is 2 times greater than "f" }}
String methods: Simple string methods --> charAt(index)
-returns the character at the specified index from this string. -index starts at 0 ex: String lname = "Chatmon" lname.charAt(4); gives back: m
String methods Methods for working with string indexes --> indexOf(ch, fromIndex)
-returns the index of the first occurrence of ch after fromIndex in the string. returns -1 if not matched. ex: import java.io.*; public class Test { public static void main(String args[]) { String Str = new String("Welcome to Tutorialspoint.com"); System.out.print("Found Index :" ); System.out.println(Str.indexOf( 'o', 5 )); } } gives back: 9
String methods Methods for working with string indexes --> indexOf(ch)
-returns the index of the first occurrence of ch in the string. Returns -1 if not matched. ex: package com.tutorialspoint; import java.lang.*; public class StringDemo { public static void main(String[] args) { String str = "This is tutorialspoint"; // returns the index of occurrence of character s System.out.println("index of letter 's' = " + str.indexOf('s')); // returns -1 as character e is not in the string System.out.println("index of letter 'e' = " + str.indexOf('e')); } } gives back: index of letter 's' = 3 index of letter 'e' = -1
String methods Methods for working with string indexes --> indexOf(s, fromIndex)
-returns the index of the first occurrence of string s in this string after fromIndex. returns -1 if not matched. ex: package com.tutorialspoint; import java.lang.*; public class StringDemo { public static void main(String[] args) { String str1 = "Collections of tutorials at tutorials point"; /* search starts from index 10 and if located it returns the index of the first character of the substring "tutorials" */ System.out.println("index = " + str1.indexOf("tutorials", 10)); /* search starts from index 9 and returns -1 as substring "admin" is not located */ System.out.println("index = " + str1.indexOf("admin", 9)); } } gives back: index = 15 index = -1
String methods Methods for working with string indexes --> indexOf(s)
-returns the index of the first occurrence of string s in this string. returns -1 if not matched ex: String str = "Here there everywhere"; int a = str.indexOf("there"); // a is 5 int b = str.indexOf("er"); // b is 1 int c = str.indexOf("eR"); // c is -1, "eR" is not found
String methods Methods for working with string indexes --> lastIndexOf(ch, fromIndex)
-returns the index of the last occurrence of ch before fromIndex in this string. returns -1 if not matched. ex: import java.io.*; public class Test { public static void main(String args[]) { String Str = new String("Welcome to Tutorialspoint.com"); System.out.print("Found Last Index :" ); System.out.println(Str.lastIndexOf( 'o', 5 )); } } gives back: Found Last Index :4
String methods Methods for working with string indexes --> lastIndexOf(ch)
-returns the index of the last occurrence of ch in the string. returns -1 if not matched ex: import java.io.*; public class Test { public static void main(String args[]) { String Str = new String("Welcome to Tutorialspoint.com"); System.out.print("Found Last Index :" ); System.out.println(Str.lastIndexOf( 'o' )); } } gives back: Found Last Index :27
String methods Methods for working with string indexes --> lastIndexOf(s, fromIndex)
-returns the index of the last occurrence of string s before fromIndex. returns -1 if not matched ex: String str = "This is tutorialspoint"; /* returns positive value(last occurrence of character t) as character is located, which searches character t backward till index 14 */ System.out.println("last index of letter 't' = " + str.lastIndexOf('t', 14)); /* returns -1 as character is not located under the give index, which searches character s backward till index 2 */ System.out.println("last index of letter 's' = " + str.lastIndexOf('s', 2)); // returns -1 as character e is not in the string System.out.println("last index of letter 'e' = " + str.lastIndexOf('e', 5)); } gives back: last index of letter 't' = 10 last index of letter 's' = -1 last index of letter 'e' = -1
String methods Methods for working with string indexes --> lastIndexOf(s)
-returns the index of the last occurrence of string s. returns -1 if not matched. ex: public class LastIndexOfExample{ public static void main(String args[]){ String s1="this is index of example";//there are 2 's' characters in this sentence int index1=s1.lastIndexOf('s');//returns last index of 's' char value System.out.println(index1);//6 gives back: 6
String methods: Simple string methods --> length()
-returns the number of characters in this string -when using method length(), the count starts at 1 and includes any spaces. ex: String lname = "Chatmon" lname.length(); gives back: 7
String methods Methods to obtain strings --> substring(beginIndex, endIndex)
-returns the strings substring that begins at the specified begin index and extends to the character at index endIndex -1. -the character at endIndex is not part of the substring -index starts at 0 ex: given --> String message = "Welcome to java" message.subtring(0,11) gives back: "Welcome to " (including spaces)
String methods Methods to obtain strings --> substring(beginIndex)
-returns the strings substring that begins with the character at the specified beginIndex and extends to the end of the string. -index starts at 0 ex: given --> String message = "Welcome to java" message.subtring(11) gives back: "Java"
String methods Methods for comparing strings --> startsWith(prefix)
-returns true if the string with the specified prefix, else false. ex: import java.io.*; public class Test { public static void main(String args[]) { String Str = new String("Welcome to Tutorialspoint.com"); System.out.print("Return Value :" ); System.out.println(Str.startsWith("Welcome") ); System.out.print("Return Value :" ); System.out.println(Str.startsWith("Tutorials") ); } } gives back: true, false
String methods Methods for comparing strings --> endsWith(suffix)
-returns true if this string ends with the specified suffix, else false ex: public class EndsWithExample{ public static void main(String args[]){ String str1 = new String("This is a test String"); String str2 = new String("Test ABC"); boolean var1 = str1.endsWith("String"); boolean var2 = str1.endsWith("ABC"); boolean var3 = str2.endsWith("String"); boolean var4 = str2.endsWith("ABC"); System.out.println("str1 ends with String: "+ var1); System.out.println("str1 ends with ABC: "+ var2); System.out.println("str2 ends with String: "+ var3); System.out.println("str2 ends with ABC: "+ var4); } } gives back : str1 ends with String: true str1 ends with ABC: false str2 ends with String: false str2 ends with ABC: true
String methods Methods for comparing strings --> equals(s1)
-returns true if this string is equal to string s1, else false. ex: given ---> String s1 = new String("HELLO"); String s2 = new String("HELLO"); System.out.println(s1.equals(s2)); gives back: true
String methods Methods for comparing strings --> equalsIgnoreCase(s1)
-returns true if this string is equal to string s1; it is case insensitive, else false. ex: given --> String s1="javatpoint"; String s2="javatpoint"; String s3="JAVATPOINT"; String s4="python"; System.out.println(s1.equalsIgnoreCase(s2)); //true because content and case both are same System.out.println(s1.equalsIgnoreCase(s3)); //true because case is ignored System.out.println(s1.equalsIgnoreCase(s4)); //false because content is not same }} gives back: true, true, false
String methods Methods for comparing strings --> compareToIgnoreCase(s1)
-same as compare to except that the comparison is case insensitive.
String methods Methods for comparing strings --> isEmpty()
-this method returns true if length() is 0, else false ex: package com.tutorialspoint; import java.lang.*; public class StringDemo { public static void main(String[] args) { String str = "tutorialspoint"; // prints length of string System.out.println("length of string = " + str.length()); // checks if the string is empty or not System.out.println("is this string empty? = " + str.isEmpty()); } } gives back: length of string = 14 is this string empty? = false
After the execution of the following code, what will be the value of num if the input values are 0? (Assume that console is a Scanner object initialized to the standard input device.) int num = console.nextInt(); if (num > 0) num = num + 13; else if (num >= 3) num = num + 15;
0
What is the output? System.out.println( ("I Love Java").length() );
11
If the String variable str contains the string "Now is the time", what is the result of the folllowing epression? String str = "Now is the time"; System.out.println(str.length() + " " + str.substring(1,3));
15 ow
Suppose the following strings are declared as follows: String city = "Tallahassee"; String state = "Florida"; What is the results of the following expressions? city.concat(state).lastIndexOf('a')
17
Suppose that you have the following code: int sum = 0; int num = 8; if (num < 0) sum = sum + num; else if (num > 5) sum = num + 15; After this code executes, what is the value of sum?
23
Suppose that s1, s2, and s3 are three strings, given as follows: String s1 ="Tallahassee, FL"; String s2 = "Atlanta, GA"; String s3 = "Birmingham, AL"; What is the results of the following expressions? s2.substring(3).lastIndexOf('a')
3
What is the output of the following Java code? int x = 57; int y = 3; switch (x % 9) { case 0: case 1: y++; case 2: y = y - 2; break; case 3: y = y + 2; case 4: break; case 5: case 6: y = y + 3; } System.out.println(y);
5
What is the output? System.out.print( ("ABCDABC").lastIndexOf("BC") );
5
int x, y; if (x < 4) y = 2; else if (x > 4) { if (x > 7) y = 4; else y = 6; } else y = 8; Based on the code above, what is the value of y if x = 4?
8
if (quotaAmt > 100 || sales > 100 && productCode == "C") bonusAmt = 50; When the above code is executed, which operator is evaluated first?
==
What is the output? System.out.println("Happy".substring(0,3));
Hap
Logical (Boolean) operator NOT (!p)
Java expression: !p logical expression: not p meaning: !p is false if p is true !p is true if p is false
Logical (Boolean) operator: AND (&&)
Java expression: p && q logical expression: p and q meaning: p && q is true if both p and q are true, false otherwise
Logical (Boolean) operator: OR (||)
Java expression: p || q logical expression: p or q meaning: p || q is true if either p or q or both are true, false otherwise
Logical (Boolean) operator EXCLUSIVE OR (^)
Java expression: p^q logical expression: p exclusive or q meaning: p^q is true when exactly one is true, false otherwise
What is the code that will display the middle initial 'L' (right justified) with a total of 10 spaces, given the following declaration? String middleName = "Lanette";
System.out.printf("Here is the first character of the middle name: %10c", middleName.charAt(0));
Suppose that s1, s2, and s3 are three strings, given as follows: String s1 ="Welcome to Java"; String s2 = "Programming is fun"; String s3 = "Welcome to Java"; What is the results of the following expressions? s1.concat(s2)
Welcome to JavaProgramming is fun
What is the output of the following code segment? String homeTown = "Tallahassee Florida"; System.out.println( homeTown.charAt(6) );
a
escape sequence for special characters \b
backspace
escape sequence for special characters \\
blackslash
escape sequence for special characters \r
carriage return
Relational operators can compare values of type ________?
char
System.out.println("Your name is " + yourName); The above statement is an example of ____, which is used to join Strings.
concatenation
character class methods toLowerCase(ch)
description: Returns the lowercase of the specified character example: import java.lang.*; public class CharacterDemo { public static void main(String[] args) { // create 4 char primitives char ch1, ch2, ch3, ch4; // assign values to ch1, ch2 ch1 = 'P'; ch2 = 's'; // assign lowercase of ch1, ch2 to ch3, ch4 ch3 = Character.toLowerCase(ch1); ch4 = Character.toLowerCase(ch2); String str1 = "Lowercase of " + ch1 + " is " + ch3; String str2 = "Lowercase of " + ch2 + " is " + ch4; // print ch3, ch4 values System.out.println( str1 ); System.out.println( str2 ); } } gives back: Lowercase of P is p Lowercase of s is s
character class methods toUpperCase(ch)
description: Returns the uppercase of the specified character example: import java.lang.*; public class CharacterDemo { public static void main(String[] args) { // create 4 char primitives char ch1, ch2, ch3, ch4; // assign values to ch1, ch2 ch1 = '4'; ch2 = 'q'; // assign uppercase of ch1, ch2 to ch3, ch4 ch3 = Character.toUpperCase(ch1); ch4 = Character.toUpperCase(ch2); String str1 = "Uppercase of " + ch1 + " is " + ch3; String str2 = "Uppercase of " + ch2 + " is " + ch4; // print ch3, ch4 values System.out.println( str1 ); System.out.println( str2 ); } } gives back: Uppercase of 4 is 4 Uppercase of q is Q
character class methods isDigit(ch)
description: Returns true if the specified character is a digit. import java.lang.*; example: public class CharacterDemo { public static void main(String[] args) { // create 2 char primitives ch1, ch2 char ch1, ch2; // assign values to ch1, ch2 ch1 = '9'; ch2 = 'V'; // create 2 boolean primitives b1, b2 boolean b1, b2; // assign isDigit results of ch1, ch2 to b1, b2 b1 = Character.isDigit(ch1); b2 = Character.isDigit(ch2); String str1 = ch1 + " is a digit is " + b1; String str2 = ch2 + " is a digit is " + b2; // print b1, b2 values System.out.println( str1 ); System.out.println( str2 ); } } gives back: 9 is a digit is true V is a digit is false
character class methods isLetter(ch)
description: Returns true if the specified character is a letter example: import java.lang.*; public class CharacterDemo { public static void main(String[] args) { // create 2 char primitives ch1, ch2 char ch1, ch2; // assign values to ch1, ch2 ch1 = 'A'; ch2 = '9'; // create 2 boolean primitives b1, b2 boolean b1, b2; // check if ch1, ch2 are letter or not and assign results to b1, b2 b1 = Character.isLetter(ch1); b2 = Character.isLetter(ch2); String str1 = ch1 + " is a letter is " + b1; String str2 = ch2 + " is a letter is " + b2; // print b1, b2 values System.out.println( str1 ); System.out.println( str2 ); } } gives back: A is a letter is true 9 is a letter is false
character class methods isLetterOrDigit(ch)
description: Returns true if the specified character is a letter or digit example: import java.lang.*; public class CharacterDemo { public static void main(String[] args) { // create 2 char primitives ch1, ch2 char ch1, ch2; // assign values to ch1, ch2 ch1 = 'A'; ch2 = '1'; // create 2 boolean primitives b1, b2 boolean b1, b2; /** * check if ch1, ch2 are letter or digit and assign * results to b1, b2 */ b1 = Character.isLetterOrDigit(ch1); b2 = Character.isLetterOrDigit(ch2); String str1 = ch1 + " is a letter/digit is " + b1; String str2 = ch2 + " is a letter/digit is " + b2; // print b1, b2 values System.out.println( str1 ); System.out.println( str2 ); } } gives back: A is a letter/digit is true 1 is a letter/digit is true
character class methods isLowerCase(ch)
description: Returns true if the specified character is a lowercase letter example: import java.lang.*; public class CharacterDemo { public static void main(String[] args) { // create 2 char primitives ch1, ch2 char ch1, ch2; // assign values to ch1, ch2 ch1 = 'A'; ch2 = 'a'; // create 2 boolean primitives b1, b2 boolean b1, b2; // check if ch1, ch2 are in lowercase and assign results to b1, b2 b1 = Character.isLowerCase(ch1); b2 = Character.isLowerCase(ch2); String str1 = ch1 + " is a lowercase character is " + b1; String str2 = ch2 + " is a lowercase character is " + b2; // print b1, b2 values System.out.println( str1 ); System.out.println( str2 ); } } gives back: A is a lowercase character is false a is a lowercase character is true
character class methods isUpperCase(ch)
description: Returns true if the specified character is an uppercase letter. example: import java.lang.*; public class CharacterDemo { public static void main(String[] args) { // create 2 char primitives ch1, ch2 char ch1, ch2; // assign values to ch1, ch2 ch1 = 'K'; ch2 = '\u0e16'; // represents THAI CHARACTER THO THUNG // create 2 boolean primitives b1, b2 boolean b1, b2; // check if ch1, ch2 are uppercase and assign results to b1, b2 b1 = Character.isUpperCase(ch1); b2 = Character.isUpperCase(ch2); String str1 = ch1 + " is uppercase character is " + b1; String str2 = "ch2 is uppercase character is " + b2; // print b1, b2 values System.out.println( str1 ); System.out.println( str2 ); } } gives back: K is uppercase character is true ch2 is uppercase character is false
escape sequence for special characters \"
double quote
Relational operator ==
equal to
A computer program will recognize both = and == as the equality operator.
false
In Java, || has a higher precedence than &&.
false
Suppose that s1, s2, and s3 are three strings, given as follows: String s1 ="Welcome to Java"; String s2 = "Programming is fun"; String s3 = "Welcome to Java"; What is the results of the following expressions? s2.startsWith("Wel")
false
Suppose that the input is 6 and console is a Scanner object initialized to the standard input device. Consider the following code. int alpha = 7; int beta = console.nextInt(); switch (beta) { case 5: alpha = alpha + 1; case 6: alpha = alpha + 2; case 7: alpha = alpha + 3; default: alpha = alpha + 5; } System.out.print(alpha); The output of this code is 9.
false
The following code segment correctly tests for equality: String month = "October"; if (month == "October") { System.out.println("The month is October."); }
false
What is the output for the following code segment? char middleInit = 'L'; System.out.println( Character.isLowerCase(middleInit) );
false
escape sequence for special characters \f
formfeed
Relational operator >
greater than
Relational operator >=
greater than or equal to
selection statements if-else-if
if (condition) statement; else if (condition) statement; . . else statement; *A user can decide among multiple options. The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that if is executed, and the rest of the ladder is by-passed. If none of the conditions are true, then the final else statement will be executed.
selection statements if
if (condition){ statement (s); } *can only execute if inside is true *if the condition is true then the statements inside the if block will be executed
selection statements if-else
if (expression){ StatementA; <--- will execute when true } else{ StatementB; <--- will execute when A not true } *If the condition is true then the statements inside the if block will be executed and if the condition is false then the statements inside the else block will be executed.
Relational operator <
less than
Relational operator <=
less than or equal to
escape sequence for special characters \n
linefeed
+ operator to concatenate strings
name = fname + lname; output: MarySmith
Relational operator !=
not equal to
format specifier %12s
output: Out the string with width at least 12 characters. If the string item has fewer than 12 characters, add spaces before the string. If the string item has more than 12 characters, the width is automatically increased. example: String fname = "Mary"; System.out.printf("The first name is: %12s \n", fname); Output: The first name is: Mary
Format specifiers- printf %6b
output: Output the Boolean value and add one space before the false value and two spaces before the true value. example: String s1 = "painting"; String s2 = "Painting"; System.out.printf("The truth value is: %6b \n", s1.equals(s2)); Output: The truth value is: false
Format specifiers- printf %5c
output: Output the character and add four spaces before the character item, because the width is 5. example: char initial ='L'; System.out.printf("Here is the character: %5c \n", initial); Output: Here is the character: L
Format specifiers- printf %10.2f
output: Output the floating-point item with width at least 10 including a decimal point and two digits after the point. Thus, there are 7 digits allocated before the decimal point. • If the number of digits before the decimal point in the item is <7, add spaces before the number. • If the number of digits before the decimal point in the item is >7, the width is automatically increased. example: double amount = 157893.4556; System.out.printf("The amount is: %10.2f \n", amount); Output: The amount is: 157893.46 The amount is: 893.48 The amount is: 7.52
format specifiers- printf %5d
output: Output the integer item with width at least 5. If the number of digits in the item is <5, add spaces before the number. If the number of digits in the item is >5, the width is automatically increased. example: int age = 45; System.out.printf("The age is: %10d \n", age); Output: The age is: 45
Printf specifiers %b
output: a boolean value example: true or false
Printf specifiers %c
output: a character example: "a"
Printf specifiers %d
output: a decimal integer example: 200
Printf specifiers %f
output: a floating-point number example: 45.460000
Printf specifiers %e
output: a number in standard scientific notation example: 4.556000e+01
Printf specifiers: %s
output: a string example: "Java is cool"
selection statements switch
switch (switch-expression) { case value1: statement(s)1; break; case value2: statement(s)2; break; ... case valueN: statement(s)N; break; default: statement(s)-for-default; } *Switch statement: A selection control structure for multiway branching *Switch label: "case" + constant which labels a code segment *Switch expression: The integral expression whose value determines which switch label is selected *The value of Switch expression that determines which branch is executed must be of types byte, char, short, int, or String
escape sequence for special characters \t
tab
When using the prewritten equals() method, a true or false comparison between two Strings is returned, but you do not know how the code looks behind the scenes.
true
Similarities of loops:
while (loop-continuation-condition) { // Loop body } = for ( ; loop-continuation-condition; ) // Loop body } ------------------------------------- for (initial-action; loop-continuation-condition; action-after-each-iteration) { // Loop body; } = initial-action; while (loop-continuation-condition) { // Loop body; action-after-each-iteration; }
Assume x=4 and y=5, which of the following is true?
x != 4 ^ y == 5
Assume x=4, which of the following is true?
x != 5
Assume x = 4 and y = 5, which of the following is true?
x < 5 || y < 5
What is the output of the following Java code? int x = 0; if (x > 0) System.out.println("positive "); System.out.print("zero "); System.out.println("negative");
zero negative
