Java Data Types
import java.awt.*;
Public class example {
boolean abool = true;
char letter = 'A';
byte abyte;
short ashort;
int aint = 0;
long along = 123456000;
Long anotherL = 123456000 ; // Unsigned 64 bits
float afloat = 33.55f;
double adouble = Math.PI;
String astring = "This is a string.";
Color acolor = Color.RED;
}
Conditionals
# Example conditionals
public class howold {
public static void main (String[] args) {
String name;
int age;
Scanner in = new Scanner(System.in);
System.out.println ("Hello, Please enter your name and age.");
name = in.nextLine();
age = in.nextInt();
System.out.println ("Hello, " + name + ", \n\tyou are " + age + " years old.");
if (age < 3) {
System.out.println ("Are you sure?");
}
}
}
# more examples
public class howold {
public static void main (String[] args) {
String s = "";
if ( s == "string" ) {
System.out.println ("This is a string.");
} else if ( s == "not a string" ) {
System.out.println ("This is not a string.");
} else {
System.out.println ("What is this?");
}
}
}
Exercise: Print different greetings for people at different ages.
Loops
# Example loops
class example {
public static void main (String[] args) {
for (String s : args ) {
System.out.println ( s );
}
}
String s = "";
for (int i = 0; i <10; i++) {
s += 'A';
}
}
class testloops {
// Do/whil (post-test)
// While (pre-test)
// for (pre-test)
public void loopwhile () {
int loop_count = 3;
while ( loop_count > 0 ) {
System.out.println ( loop_count );
loop_count--;
}
}
public void loopdowhile () {
int loop_count = 3;
do {
System.out.println ( loop_count );
loop_count--;
} while ( loop_count > 0 );
}
}
Functions
# Example functions
public static void main (String[] args) {
thisfunc ( 3, "testfunc" );
}
public static void thisfunc ( int i, String s) {
System.out.println ( i );
System.out.println ( s );
}
Exceptions
# Example exceptions
public static void main (String[] args) {
int first;
if (args.length > 3) {
try {
first = Integer.parseInt (args[0]);
}
catch (NumberFormatException e) {
System.err.println ("Error: too many arguments.");
System.exit(1);
}
}
}
}
