The break Statement
The
break statement has two forms: labeled and unlabeled.
You saw the unlabeled form in the previous discussion of the
switch statement.
You can also use an unlabeled
break to terminate a
for,
while,
or
do-while loop, as shown in the following
BreakDemo
program:
class BreakDemo {
public static void main(String[] args) {
int[] arrayOfInts = { 32, 87, 3, 589, 12, 1076,
2000, 8, 622, 127 };
int searchfor = 12;
int i;
boolean foundIt = false;
for (i = 0; i < arrayOfInts.length; i++) {
if (arrayOfInts[i] == searchfor) {
foundIt = true;
break;
}
}
if (foundIt) {
System.out.println("Found " + searchfor
+ " at index " + i);
} else {
System.out.println(searchfor
+ " not in the array");
}
}
}
This program searches for the number 12 in an array. The
break statement, shown in boldface, terminates the
for
loop when that value is found. Control flow then transfers to
the print statement at the end of the program.
This program's output is:
An unlabeled
break statement terminates the innermost
switch,
for,
while, or
do-while statement, but a labeled
break terminates an outer statement.
The following program,
BreakWithLabelDemo
,
is similar to the previous program,
but uses nested
for loops to search for a value in a two-dimensional array.
When the value is found, a labeled
break terminates the outer
for loop (labeled "search"):
class BreakWithLabelDemo {
public static void main(String[] args) {
int[][] arrayOfInts = { { 32, 87, 3, 589 },
{ 12, 1076, 2000, 8 },
{ 622, 127, 77, 955 }
};
int searchfor = 12;
int i;
int j = 0;
boolean foundIt = false;
search:
for (i = 0; i < arrayOfInts.length; i++) {
for (j = 0; j < arrayOfInts[i].length; j++) {
if (arrayOfInts[i][j] == searchfor) {
foundIt = true;
break search;
}
}
}
if (foundIt) {
System.out.println("Found " + searchfor +
" at " + i + ", " + j);
} else {
System.out.println(searchfor
+ " not in the array");
}
}
}
This is the output of the program.
The
break statement terminates the labeled statement; it does not transfer the flow of control to the label. Control flow is transferred to the statement immediately following the labeled (terminated) statement.
The continue Statement
The
continue statement skips the current iteration of a
for,
while , or
do-while loop.
The unlabeled form skips to the end of the innermost loop's body and evaluates the
boolean expression that controls the loop.
The following program,
ContinueDemo
,
steps through a
String, counting the occurences of the letter "p".
If the current character is not a p, the
continue statement skips the rest of the loop and proceeds to the next character.
If it
is a "p", the program increments the letter count.
class ContinueDemo {
public static void main(String[] args) {
String searchMe = "peter piper picked a peck of pickled peppers";
int max = searchMe.length();
int numPs = 0;
for (int i = 0; i < max; i++) {
//interested only in p's
if (searchMe.charAt(i) != 'p')
continue;
//process p's
numPs++;
}
System.out.println("Found " + numPs + " p's in the string.");
}
}
Here is the output of this program:
Found 9 p's in the string.
To see this effect more clearly, try removing the
continue statement and recompiling. When you run the program again, the
count will be wrong, saying that it found 35 p's instead of 9.
A labeled continue statement skips the current iteration of an outer loop marked with the given label.
The following example program, ContinueWithLabelDemo, uses nested loops to search for a substring within another string.
Two nested loops are required: one to iterate over the substring and one to iterate over the string being searched.
The following program,
ContinueWithLabelDemo
, uses the labeled form of continue to skip an iteration in the outer loop.
class ContinueWithLabelDemo {
public static void main(String[] args) {
String searchMe = "Look for a substring in me";
String substring = "sub";
boolean foundIt = false;
int max = searchMe.length() - substring.length();
test:
for (int i = 0; i <= max; i++) {
int n = substring.length();
int j = i;
int k = 0;
while (n-- != 0) {
if (searchMe.charAt(j++)
!= substring.charAt(k++)) {
continue test;
}
}
foundIt = true;
break test;
}
System.out.println(foundIt ? "Found it" :
"Didn't find it");
}
}
Here is the output from this program.
The return Statement
The last of the branching statements is the
return statement.
The
return statement exits from the current method, and control flow returns to where the method was invoked.
The
return statement has two forms: one that returns a value, and one that doesn't.
To return a value, simply put the value (or an expression that calculates the value) after the
return keyword.
The data type of the returned value must match the type of the method's
declared return value. When a method is declared
void,
use the form of
return that doesn't return a value.
The
Classes and Objects
lesson will cover everything you need to know about writing methods.
