JAVA (something like C)

Object Oriented Programming Process orientated – code acting on data Object oriented – data controls access to code Encapsulation – java has a ‘class’. The data is the state and the methods (code) is the behavior. You control the methods and access to the data Inheritance – where one class acquires the properties of another class Polymorphism – one interface multiple methods

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comments A single line comment int row; // keeps track of the row multiple line comments /* this is one line of the comment this is the 2nd line this is the third line */

Documentation comments acts like multiple line comments /** this is one line of the comment this is the 2nd line this is the third line */ note the initial /** The javadoc program will collect these blocks of comments as documentation for the program javadoc filename.java

special symbols { } indicates a block of code ( ) parameters to a method [ ] indicates an array ; terminates a statement,a seperator.used to separate package names Note table of reserved words on page 39

Identifier names Start with a letter Contains letters (upper or lower case) numbers _ (the underscore) $ Can be any length No imbedded spaces or special characters Do not start an identifier with a number

Examples/Naming Conventions numberOfRows num_rows row8 Naming Conventions classes start with a capitol letter HelloWorld ShoppingCart methods & identifiers with a small letter println() getChar() constants are all caps PIE

System.out.println( ) System.out.println (….) sends a String to the monitor System.out.println(“Hi Mom”); The + ‘concatenates’ two variables int aVal = 17; System.out.println(“a = “ + aVal); System.out.println(“a=“ + aV + “ b=“ + bV)

Primitive data types JAVA has 8 primitive data type Name size | range | byte 8-bits -128 ~ 127 short 16-bits -32k ~ +32k int 32-bits -2**31 ~ +2**31 long 64-bits -2**63 ~ + 2**63

Primitive data types (cont.) Name size | range | float 32-bits X 10**38 double 64-bits X 10**308 char 16-bits 0 ~ 65,535 boolean 1-bit true or false (not a 0 or a 1)

Examples of primatives int x; int x, y=7, zz, rows=8; boolean isRunning = false; double dd; float f = 10.3; (error - defaults to a double) float fx = 22.4f; note the ‘f’ byte b1, b2 = 44, cx; short ss=5;

The char char uses a 16-bit Unicode character set The Unicode set allows 65,536 different characters. (about half are assigned) char ch = ‘a’; char ch1, ch2 = ‘7’, ch3 = ‘X’; char delta = ‘\u0394’ delta symbol char copyrt = ‘\u00AE’ copy write symbol escape seq. – page 32 (EX \t is tab)

the String class String is a class, not a primitive data type is a sequence of characters not an array of char terminated by a null immutable – cannot be changed once created String ss; String s1 = “hi mom”; String s1, su=“XXX”, s3=“SDE”;

Java DOS commands Javac A:\>javac test.java –compiler –uses a text file named ????.java –creates a ????.class file of byte code java A:\>java test –the interpreter (runs the class code) –runs an application appletviewer A:\>appletviewer test.html –runs an applet

Minimum JAVA program class Skeleton { public static void main(String args[]) { } // end main } // end class

arithmetic Expression – series of variables (methods) that evaluate to a single variable = assign (evaluate right, assign to right) + add x = x + 7; - subtractx = 8 – cx; * multiplypay = rate * time; /dividetax = too_much / 1.0; %remainder (mod) row = x % 4; row is the remainder of x / 4 ans = 33 % 6; ans is 3

Consider the primitives byte 8 bits short 16 bits int 32 bits long 64 bits float 32 bits double 64 bits char 16 bits

Some examples Define and initialize all the primitives Add the following to skeleton and compile short = byte; byte = short; double = float float = double; int = boolean; int = short * byte; int = short * float; double = int * double; float = short * double; int = char; chat = int;

Conversion and casting Automatic – types are compatible destination is larger than the source Casting (target type) value byte b = (byte) someValue; byte b = intExample; error byte b = (byte) intExample; OK byte b = 50; byte x = b/2; Error Byte x = (byte)(b/2); ok

Shortcuts in arithmetic Shortcuts x++ x = x + 1; x--x = x – 1; x+=7;x = x + 7; x*=3;x = x * 3; x/=2;y = y / 2; q-=5;q = q – 5;

ternary expression expression01 ? expression02 : expression03 Expression01 must evaluate to a boolean If expression01 is true, expression 02 is evaluated, else expression03 is evaluated

Example of ? : if (x > y) max = x; else max = y; is the same as max = x>y ? x : y;

‘pre’ & ‘post’ Difference between x++; and ++x; Example int x = 5; System.out.println(x + “ “ + x++); int x = 5; System.out.println(x + “ “ + ++x);

Operator precedence Do work within ( ) Then, left to right… * / % + - = What’s the answer to the following.. n = * ;

if statement if(expression) // expression is evaluated block of code// execute if true else block of code// execute if false Note – a block of code can contain a nested if statement

examples if (x > 6) System.out.println(“x is bigger); else System.out.println(“x is less than 6); if (x>8) {} else System.out.println(“x is less than 8”);

logical operators &evaluate both, both must be true |evaluate both, either must be true && both must be true. If 1 st is false, do not evaluate the 2 nd ||one must be true. If 1 st is true, do not evaluate the 2 nd ~ tilda - not Shift and bit-wise operators – you are on your own (page 80)

&& and & if ((a>b) & (c<=7)) System.out.println(“both true”); else System.out.println(“one not true”); if ((a>b) && (c<=7)) System.out.println(“both true”); else System.out.println(“one not true”);

|| and | if ((a>b) | (c<=7)) System.out.println(“at least one true”); else System.out.println(“both false”); if ((a>b) || (c<=7)) System.out.println(“at least one true”); else System.out.println(“both false”);

if ((a>b) && (a++)) System.out.println(“(true)a=” + a); else System.out.println(“(false)a=” + a); if (a>b) if (c!=7) System.out.println(“123456”); is the same as If((a>b) & (c!=7)) System.out.println(“123456”);

Relational operators ==equal to !=not equal >greater than <less than >=greater than or equal to <=less than or equal to

The loops For a loop you need 3 things a counter of some kind a comparison statement - a test increment the counter some time the loops are

for loop for (int i = 6; i<5; i++) { System.out.println(“counter is “ + i); } the ‘for’ statement contains the counter, increment, and test all together

example For (int k=0; k<3; k++) System.out.println(k); for (int d=5; d<3; d++) System.out.println(k); for (int d=3, int e=7; d<e; d++, e--) System.out.println(d + “ and e=“ + e);

for loop – using a comma for (a =1, b=4; a<b; a++, b--) { System.out.println(“a = “ + a); System.out.println(“b = “ + b); } Gives a = 1 – b = 4 – a = 2 – b = 3

for loop – some variations boolean done = false; for (a =1; !done; a++) { ……… done = true; } boolean done = false; for ( ; !done; ) { ……… done = true; }

while loop int x=0; // counter while (x<5) // test { System.out.println(“counter = “ + x); x++; // increment }

Example #1 int x=4; // counter while (x<5) // test { System.out.println(“counter = “ + x); x++; // increment }

Example #2 int x=4; // counter while (x<5) // test { System.out.println(“counter = “ + x); }

Example #3 int x=14; // counter while (x<5) // test { System.out.println(“counter = “ + x); x++; // increment }

do/while loop int c=3; // counter do { System.out.println(“counter = “ + c); c++; // increment } while (c<5); // test what’s ‘special’ about a do/while loop??

Example #1 int c=3; // counter do { System.out.println(“counter = “ + c); } while (c<5); // test

Example #2 int c=13; // counter do { System.out.println(“counter = “ + c); c++; // increment } while (c<5); // test

Switch statement switch(expression) { case value01:statement; break; case value02:statement; break; default: statement; } The expression is evaluated. Jump to the corresponding case statement with = value

expression must be a byte, short, int, or char When you jump to the proper case value, you execute code until the end of the switch statement or a break statement is executed No matches – jump to default No default – out of switch

Switch(month) { case 1:days=31; break; case 2:days=28; break; case 3: days=31; break; case 4: days=30; break; | case 12:days=31; break; default: days=0; }

switch(month) { case 9: case 4: case 6: case 11:days=30; break; case 2: days=28; break; default: days=31; }

More use of “break” hitting a ‘break’ will terminate a loop for(int x=0; x<100; x++) { if (x==5) break; System.out.println(“X=“ + x); } X=0 X=1 X=2 X=3 X=4

Using ‘break’ in nested loops for(int x=1; x<4; x++) { System.out.println(“X=“ + x); for (int y=0; y<30; y++) { if (y==x) break; System.out.println} (“Y=“ + y); }

“break” with the while loop while (x<100 { if (x==5) break; System.out.println(“X=“ + x); x++; } X=0 X=1 X=2 X=3 X=4

break with a label outer: for(i=1; i<100; i++) { for (j=4; j<50; j++) { ……. if((j%i)==0) break outer; …….. } // end j for loop } // end i for loop

continue statement for (int x=0; x<8; x++) { System.out.print(x + “ “); if(x%2) continue; System.out.println(“ “); }

break / continue / go to break and continue may specify a label a label is a JAVA identifier that indicates a block of code aLabel: { stuff; } It is close to a GoTo. Don’t use it;