A loop continues until a condition is reached. And control falls through each case in a switch. With break, a keyword, we stop control flow.
No further iterations in a loop will occur after a break is reached. Continue, meanwhile, will stop just the current iteration.
For-loop breakThis program uses the break statement in a for-loop. We loop over 100 numbers from 0 to 99. But when 5 is reached, a break statement executes.
break is a way to stop a loop, eve none that has not reached its bounds.break statement has no arguments. We cannot use labels with it. We cannot use it to break out of nested loops at once.break (but the enclosing method returns also).public class Program {
public static void main(String[] args) {
// Loop over the first 100 integers.
for (int i = 0; i < 100; i++) {
System.out.println(i);
// Break when the variable equals 5.
if (i == 5) {
break;
}
}
}
}0
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5While-true loopBreak is most useful in while-loops. Here we use a while-true loop, which repeats infinitely until broken. If the random number is low, we break the loop.
while-loop is more intuitive for students than using for-loops.public class Program {
public static void main(String[] args) {
// Use a while-true loop.
while (true) {
double number = Math.random();
System.out.println(number);
// Break if random number is less than a certain value.
if (number <= 0.2) {
break;
}
}
}
}0.5650302991616442
0.64936100765301
0.18994610761919195breakA switch statement has case blocks. If a break (or return) statement does not terminate a case, control will fall through to the next case.
break in case 0. But case 1 has a break. So when we switch on 0, id is incremented twice.public class Program {
static int getId(int index) {
int id = 0;
switch (index) {
case 0:
// No break is in this case block, so control falls through.
id++;
case 1:
// Control breaks in this block.
id++;
break;
case 2:
// Set id to 100.
id = 100;
}
return id;
}
public static void main(String[] args) {
int id = getId(0);
System.out.println(id);
id = getId(1);
System.out.println(id);
id = getId(2);
System.out.println(id);
}
}2
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100breakHere we test the performance of a break statement in a loop. The two loops (sum1 and sum2) are not precisely equivalent.
break statement, and the loop design is simpler.break-keyword. Break may cause a slowdown.public class Program {
static int sum1(int max, int[] array) {
// Loop over range in a for-loop.
int sum = 0;
for (int i = 0; i < max; i++) {
sum += array[i];
}
return sum;
}
static int sum2(int max, int[] array) {
// Loop over entire array, and use break to stop.
int sum = 0;
for (int i = 0; i < array.length; i++) {
if (i >= max) {
break;
}
sum += array[i];
}
return sum;
}
public static void main(String[] args) {
int[] values = { 10, 20, 30, 40, 50, 60, 70, 80 };
long t1 = System.currentTimeMillis();
// Version 1: use for-loop with range.
for (int i = 0; i < 100000000; i++) {
sum1(5, values);
}
long t2 = System.currentTimeMillis();
// Version 2: use for-loop with range and break.
for (int i = 0; i < 100000000; i++) {
sum2(5, values);
}
long t3 = System.currentTimeMillis();
// ... Times.
System.out.println(t2 - t1);
System.out.println(t3 - t2);
}
} 5 ms, sum1: For-loop
254 ms, sum2: For-loop with breakBreak is an important keyword in Java. It affects the flow of control. It influences what statements are next reached, in a loop or in a switch.
Other control statements, like continue or return, may take the place of break. These statements create branches in code. They change the next statement executed.