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What is the if statement?
"Probable-Possible, my black hen,
She lays eggs in the Relative When.
She doesn't lay eggs in the Positive Now
Because she's unable to postulate how."
-- Frederick Winsor
If examples
• if (age > 65) stopPayingSocialSecurity = true;
if (youAteLotsOfFood)
youGetFat = true;
if (grade < 65)
letterGrade = “F”;
if else examples
• if (grade < 65)letterGrade = “F”;
else if ((grade > 65) && (grade < 70))
letterGrade = “D”;
else if ((grade >= 70) && (grade < 80))
letterGrade = “C”; // etc....
Making If handle multiple statements..
• if (theCowsComeHome) {statement1;
System.out.println(“moo”);
} else {
// this is called a block of code
theOtherThingYouMightDo;
}
Conditional Operator
letterGrade = (grade < 65) ? “F” : “pass”;
Good for assignments with many simple boolean decisions.
The While statement
• Why should I use the while statement?– Do something as long as some condition is met.
• int i = 10;
while ( i >= 0) {
System.out.println(i);
i = i – 1;
}
Do statement
• Why do I need the do statement?
• int i=0;
do {
System.out.println(i++);
} while (!(i > 10));
Do{….} while(In.getBoolean(“continue?”));
while example
• while (userWantsToContinue) {– keepDoingStuff;
• }
• while (weHaveMoreData) {– keepDoingDataProcessing;
• }
for statement
• for (init; booleanCondition; iter) {• }• for (int i=0; i <= 10; i++)
System.out.println(i);/// as an alternativeInt i=0; //just like a while….While (i<=10){System.out.println(i++);
}
Continue
continue is a reserved word.
Continue alters the flow of control
Continue must reside in a continue target.
Some continue targets are:
WHILE, DO, FOR, SWITCH
What does continue do?
• Makes the target go to the next value.
for(int i=0; i < 10; i++) {
if (i < 5) continue;
System.out.println(i); // prints 5..9
}
Cont. in While
int i=0;
while (i < 10) {
i++;
if ((i % 2) = =0) continue;
System.out.println(i);
} // 1 .. 9
do continue!
int i=0;
do {
i++;
if ((i % 2) == 1) continue;
System.out.println(i);
} while(i < 10); //2..10
Break
• Break is a Java keyword
• Makes the target terminate.
• Must be in a break target.
• for, while, do, switch
Break example
for(int i=0; i < 10; i++) {
if (i < 5) break;
System.out.println(i); // prints NOTHING
}
while-break
int i=0;
while (i < 10) {
i++;
if ((i % 2) = =0) break;
System.out.println(i);
} // prints 1
do-break
int i=0;
do {
i++;
if ((i % 2) == 1) break;
System.out.println(i);
} while(i < 10); //prints nothing
labeled Continue
start: for (int i=0; i < 10; i++) {for (int j=0; j < 10; j++) {
System.out.println(i+j);
if (i + j > 10) continue start;
}
}//doubly nested for-loop with labeled continue.
labeled break
start: for (int i=0; i < 10; i++) {for (int j=0; j < 10; j++) {
System.out.println(i+j);
if (i + j > 10) break start;
}
}//doubly nested for-loop with labeled break.
// prints 0..9,1..10, 2..11 then stops.
switch statement
• switch – reserved word
• switch – makes a table out of several different statements and selects which ones get executed. Like a complex if-else.
Switch Example
int i = 10;
switch(i) {
case 2: {
statement;
break;
}
case 10: {
statement;
break;
}
}
switch on char
char a = ‘q’
switch (a) {
case ‘q’: {
quit();
break;
}
case ‘s’: {
save();
break;
}
}
default
• default is a keyword
• default appears in switch statements
• default is used when no case is satisfied
Example default
char a = ‘z’
switch (a) {
case ‘q’: {
System.out.println(“quit”);
break;
}
default: {
System.out.println(“command not found”);
break;
}
}
return
• return is a reserved word.
• causes a sudden change in the flow of control to the invoking method.
example of return
public static void main(String args[]) {
System.out.println(“this is the return example”);
return;
}
example of return
public static void main(String args[]) {
double x = 10 * Math.cos(Math.PI);
if (x > 20) return;
System.out.println(x);
}
My first method using return
public static int addOne(int x) {return x + 1;
}
public static void main(String args[]) {
System.out.println(addOne(1));
}
degs to rad example
public static double deg2rads(double d) {return d * Math.PI / 180.0;
}
public static void main(String args[]) {
System.out.println(deg2rads(180));
}
F2C
public static double f2c(double f) {return (5.0/9.0) * (f –32);
}
public static void main(String args[]) {
System.out.println(f2c(212));
}
future value of an investment
public static double fv(
double p, double r, double y) {return p * Math.pow(1+r,y);
}
public static void main(String args[]) {
System.out.println(fv(100,0.07,30));
}