1. CS 200 More Primitives, Objects, Branches and Methods
Jim Williams, PhD

2. This Week pre-Exam1: Results - emailed In-class review
Exam 1: Alternatives - soon
Programs: P4 due Thursday
Lab: Branches, Eclipse & Styling
Lecture: More Primitives, Objects, Branches & Methods

3. Are these equivalent? boolean tired = true; boolean tired = true;
Same result in all cases
Different result sometimes
Error
boolean tired = true;
if ( tired) {
//take break
tired = false; }
if ( !tired) {
//keep working
boolean tired = true;
if ( tired) {
//take break
tired = false;
} else {
//keep working }

4. Floating Down a River

5. Side Trip, maybe multiple side trips
boolean tired = true;
if ( tired) {
System.out.println(“take break”); }

6. One side of the Island or the other
boolean sunny = false;
if ( sunny) {
System.out.print(“sunny”);
} else {
System.out.print(“not sunny”); }
System.out.println( “ and back together”);

7. Equivalent? Yes No char chr = //any valid char out = 'W';
if ( chr == 'A') {
out = 'X';
} else if ( chr == 'B') {
out = 'Y';
} else {
out = 'Z'; }
char chr = //any valid
char out = 'W';
if ( chr == 'A') {
out = 'X';
} if ( chr == 'B') {
out = 'Y';
} if ( chr != 'A' || chr != 'B') {
out = 'Z'; }
Yes No

8. Switch: What is printed out?
char choice = 'a';
switch (choice) {
case 'a': System.out.print("a");
case 'b': System.out.print("b");
break;
default: System.out.print("other"); } a b ab
other

9. What is the value of msg? boolean flag = false;
String msg = "before if";
if ( flag); {
msg = "" + flag; }
before if
true
false

10. Comparing: == vs equals()
Primitive data types
use == for comparing primitive values
No equals() method for primitive data types
Reference data types
use == and !=for comparing references
use equals() for comparing instance/object contents
The meaning of equals() depends on the class it is defined in.

11. What is printed out? true *compiler error false int i = 6; int j = 6;
System.out.println( i == j);
System.out.println( i.equals( j));
Integer k = new Integer( 7);
Integer m = new Integer( 7);
System.out.println( k == m);
System.out.println( k.equals( m));
true
*compiler error
false

12. Values of a1 and a2? char ch1 = 'H'; String str = "Hello";
a1: true
a2: true
a1: false
a2: false
char ch1 = 'H';
String str = "Hello";
char ch2 = str.charAt(0);
boolean a1 = ch1 == ch2;
boolean a2 = ch1.equals(ch2);

13. String: == vs equals() String str1 = "hello"; String str2 = "hello";
String str3 = new String("hello");
String str4 = "hello";
System.out.println( str1 == "hello" );
System.out.println( str1 == str2);
System.out.println( str1.equals("hello"));
System.out.println( str3 == str1);
System.out.println( str3.equals( str2));

14. Scanner Scanner input = new Scanner("1 \ntwo \n 2\n\n");
int a = input.nextInt();
if ( input.hasNextInt()) {
int b = input.nextInt();
} else {
input.nextLine(); }
String line = input.nextLine();
System.out.println("#" + line + "#");

15. Primitive Data Types byte short int long float double char
boolean 1 bit or more
Bytes in Memory

16. Widening Primitive Conversion
Narrower to Wider
Keeps magnitude may lose some precision
byte -> short -> int -> long -> float -> double
float f = 23; //implicit conversion
double d = f; //implicit conversion
int n = (int)43.2; //must explicitly cast

17. Widening Primitive Conversion
char -> int …
Recall char is 2 bytes, non-negative:
integers are negative to positive
int num = 'C'; //implicit conversion
char ch = (char)70; //must be explicitly cast

18. What will print? 65 static void mPrint( char ch) { A
compiler error
other error
static void mPrint( char ch) {
System.out.print( ch); }
public static void main(String []args) {
mPrint( (char)65);

19. Integer Overflow int bigNum = Integer.MIN_VALUE; bigNum -= 1;
negative
non-negative
error
int bigNum = Integer.MIN_VALUE; bigNum -= 1;
String str; str = bigNum < 0 ? "negative" : "non-negative";
System.out.println( str);
try it

20. Comparing Floats equal double num1 = 10.3; double num2 = 2.2;
not equal
error
double num1 = 10.3;
double num2 = 2.2;
double num3 = num1 - num2;
if ( num3 == 8.1) {
System.out.println( "equal");
} else {
System.out.println( "not equal"); }
try it

21. Comparing Floating Point values
double num1 = 10.3;
double num2 = 2.2;
double num3 = num1 - num2;
double epsilon = 0.001;
if ( Math.abs( num ) < epsilon ) {
System.out.println( "equal");
} else {
System.out.println( "not equal"); }

22. Short-Circuit
&&
If the left side is false it doesn't matter what the right side is, so the right-side isn't evaluated. ||
If the left side is true it doesn't matter what the right side is, so the right-side isn't evaluated.

23. Short Circuit evaluation
boolean flag = true;
if ( flag || (flag = false)) {
System.out.print( "if: " + flag);
} else {
System.out.print( "else: " + flag); }
if: true
if: false
else: true
else: false
try it

24. Notes Exam Alternatives have been Emailed
to those that filled out the form
Exam Locations
Review Questions
Lecture: More on Previous 4 Chapters

25. Compound and unary operators
int i = 5;
i += 2; // i = i + 2;
if ((i += -3) < 2) { i = 3; };
i %= 2;
System.out.print( i); 1 2 3
try it

26. What is the resulting value of nums?
String nums = "3";
nums += 4 + 5;
//not equivalent due to operator precedence
nums = nums ; 3
345 12 39
try it

27. Dangling Else - What is out?
int value = 0;
String out = "abc";
if ( value >= 1 ) if ( value <= 10) out = "1 to 10";
else out = "else"; }
out: abc
out: 1 to 10
out: else
out: abcelse
try it
Else goes with nearest if. Use braces!

28. null Reference String s = null; //null reference
null is no-reference or refers to nowhere
Any Reference variable can be set to null.
String s = null; //null reference
String str = ""; //reference to 0-length string, not null
if ( str != null) {
//have valid reference }

29. null Reference Dereferencing null causes NullPointerException
Scanner in = new Scanner( System.in);
String str = null;
if ( in.hasNextInt()) {
str = in.next(); }
char ch = str.charAt(0);
System.out.println( ch);

30. What will print?, How to fix?
true
false
compiler error
runtime error
public static void printIfA(String str) {
if ( str.length()>0 && str != null)
System.out.print( str.charAt(0) == 'A'); }
Fix by changing condition to: str != null && str.length() > 0 which uses short-circuiting to avoid the right side of && when str is null.
C - compiler error is the only incorrect one.
If the argument to printIfA is "A", "a" then true or false will print
If the argument to printIfA is "" then nothing will print
If the argument to printIfA is null then runtime error

31. java.lang.String String strA = "This is a string"; //String literal
int lengthA = strA.length();
int lengthB = strA.substr(10).length();
//odd looking but works.
int lengthB =
"This is a string".substr(10).length();

32. packages: import vs. fully qualified
Fully qualified class name
java.util.Scanner input = new java.util.Scanner( System.in);
Not fully qualified so need import statement
Scanner input = new Scanner( System.in);

33. char - Which will compile?
1, 2, 3
1, 3 1
2, 3
int intValue = 0;
char aChar = 'B';
intValue = aChar; // 1
aChar = intValue + 1; // 2
aChar = '\u0041'; // 3
try it

34. Parameter Passing Java has Only Pass-by-Value
For both primitive and reference types only the value of a variable is passed as the argument.
The argument may be either a primitive or a reference.
The term Pass-by-Reference means the reference of the variable containing the value is passed as the argument.
Java does NOT have Pass-by-Reference

35. What is print out? two one two main main two one two two two one main
one two two main
static void one() {
System.out.print( "one "); }
static void two(int num) {
System.out.print("two ");
one();
public static void main( String []args) {
two( 3);
System.out.print("main ");
try it.

36. What is print out? grape apple banana
public static void showFruit( String name) {
name = new String("apple");
new String("banana"); }
public static void main(String[] args) {
String name = "grape";
showFruit( name);
System.out.println( name);
try it.

37. What prints out? print(double) static void print( double value) {
System.out.println( "print(double)"); }
static int print( int value) {
System.out.print( "print(int)");
return 1;
public static void main( String [] args) {
print( 10);
print(double)
print(int)
error
try it.

38. Method Overloading
Overloaded methods have same name but differ in number or data types of parameters.
Method signature in yellow
public static int myMethod(int a, double b) { }
Look at name and data types of arguments
int result = myMethod( 10, 23.4);

39. What prints out? print(double)
static void print( double val1, double val2) {
System.out.println( "print(double)"); }
public static void main( String [] args) {
double value = 10.0;
print( value, 20);
static void print( int val1, int val2) {
System.out.println( "print(int)");
print(double)
print(int)
error
try it.

40. What prints out? void print int print error
static void print( double val1, double val2) {
System.out.println( "void print"); }
static int print( double num1, double num2) {
System.out.print( "int print");
return 1;
public static void main( String [] args) {
print( 10.0, 20.0);
void print
int print
error
try it.

41. What prints out? print(double)
static void print( double val1, double val2) {
System.out.println( "print(double)"); }
static int something( int val1, int val2) {
System.out.print( "something(int)");
return 1;
public static void main( String [] args) {
print( 10, 20);
print(double)
something(int)
error
try it.

42. Memory Areas Stack Heap frame contains local variables and parameters
allocated on method call, freed on method return
Heap
allocated when needed, (e.g., using new)
use references to access
garbage collector frees memory no longer accessible
review
1 passing primitive to method
changing parameter in method
2 passing array to method
changing contents of array in method
3 passing array to method
changing parameter to another array in method
4 passing a string to method
calling string method in method
public class ClassNameHere {
static void method1(int num) {
num = 5; }
static void method2(int []listA) {
listA = new int[3];
listA[1] = 10;
static void method3(StringBuffer name) {
name
//name.toUpperCase();
public static void main(String[] args) {
String name = "Helen";
method3( name);
System.out.println( name);
// int [] listB = {4, 6, 8};
// method2( listB);
// System.out.println( listB[1]);
// int num = 4;
// method1( num);
// System.out.println("num=" + num);

43. Primitives and Wrapper classes
Draw a picture of memory and describe each.
public static void main( String []args) {
int k;
Integer m;
k = 2; //example of ?
m = 3; //example of ?
k = m; //example of ? }

44. Strings and memory class S { public static void main( String []args) {
String name;
new String(“dog”);
name = new String(“happy”); }

45. Where is memory allocated?
name: heap
new String("spot"): heap
name: stack
new String("spot"): stack
public static void main( String []args) {
String name;
name = new String("spot");
new String("fido"); }
B is the best answer
A, C and D are not true

46. Is result true or false? true Integer m = 5; Integer n = 5; false
boolean result = m == n;
true
false
error
A is correct. The fine print at the provided link says for Integer instances based on int literals between and 127 will have the same reference for the same int literal value. The intention of this example is to emphasize experimenting, discovering short illustrative examples and an introduction to the Java Language Specification.
Part of relevant details:
If the value p being boxed is an integer literal of type int between -128 and 127 inclusive (§3.10.1), or the boolean literal true or false (§3.10.3), or a character literal between '\u0000' and '\u007f' inclusive (§3.10.4), then let a and b be the results of any two boxing conversions of p. It is always the case that a == b.
Ideally, boxing a primitive value would always yield an identical reference. In practice, this may not be feasible using existing implementation techniques. The rule above is a pragmatic compromise, requiring that certain common values always be boxed into indistinguishable objects.
Java Language Specification