Related
I've got a nested loop construct like this:
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
// Do something and break...
break; // Breaks out of the inner loop
}
}
}
Now how can I break out of both loops? I've looked at similar questions, but none concerns Java specifically. I couldn't apply these solutions because most used gotos.
I don't want to put the inner loop in a different method.
I don't want to return the loops. When breaking I'm finished with the execution of the loop block.
Like other answerers, I'd definitely prefer to put the loops in a different method, at which point you can just return to stop iterating completely. This answer just shows how the requirements in the question can be met.
You can use break with a label for the outer loop. For example:
public class Test {
public static void main(String[] args) {
outerloop:
for (int i=0; i < 5; i++) {
for (int j=0; j < 5; j++) {
if (i * j > 6) {
System.out.println("Breaking");
break outerloop;
}
System.out.println(i + " " + j);
}
}
System.out.println("Done");
}
}
This prints:
0 0
0 1
0 2
0 3
0 4
1 0
1 1
1 2
1 3
1 4
2 0
2 1
2 2
2 3
Breaking
Done
Technically the correct answer is to label the outer loop. In practice if you want to exit at any point inside an inner loop then you would be better off externalizing the code into a method (a static method if needs be) and then call it.
That would pay off for readability.
The code would become something like that:
private static String search(...)
{
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
// Do something and break...
return search;
}
}
}
return null;
}
Matching the example for the accepted answer:
public class Test {
public static void main(String[] args) {
loop();
System.out.println("Done");
}
public static void loop() {
for (int i = 0; i < 5; i++) {
for (int j = 0; j < 5; j++) {
if (i * j > 6) {
System.out.println("Breaking");
return;
}
System.out.println(i + " " + j);
}
}
}
}
You can use a named block around the loops:
search: {
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
// Do something and break...
break search;
}
}
}
}
I never use labels. It seems like a bad practice to get into. Here's what I would do:
boolean finished = false;
for (int i = 0; i < 5 && !finished; i++) {
for (int j = 0; j < 5; j++) {
if (i * j > 6) {
finished = true;
break;
}
}
}
You can use labels:
label1:
for (int i = 0;;) {
for (int g = 0;;) {
break label1;
}
}
Use a function:
public void doSomething(List<Type> types, List<Type> types2){
for(Type t1 : types){
for (Type t : types2) {
if (some condition) {
// Do something and return...
return;
}
}
}
}
You can use a temporary variable:
boolean outerBreak = false;
for (Type type : types) {
if(outerBreak) break;
for (Type t : types2) {
if (some condition) {
// Do something and break...
outerBreak = true;
break; // Breaks out of the inner loop
}
}
}
Depending on your function, you can also exit/return from the inner loop:
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
// Do something and break...
return;
}
}
}
If you don't like breaks and gotos, you can use a "traditional" for loop instead the for-in, with an extra abort condition:
int a, b;
bool abort = false;
for (a = 0; a < 10 && !abort; a++) {
for (b = 0; b < 10 && !abort; b++) {
if (condition) {
doSomeThing();
abort = true;
}
}
}
Using 'break' keyword alone is not the appropriate way when you need to exit from more than one loops.
You can exit from immediate loop
No matter with how many loops your statement is surrounded with.
You can use 'break' with a label!
Here I've used the label "abc"
You can write your code as following, within any function in Java
This code shows how to exit from the most outer loop
abc:
for (int i = 0; i < 10; i++) {
for (int j = 0; j < 10; j++) {
for (int k = 0; k < 10; k++) {
if (k == 1){
break abc;
}
}
}
}
Also you can use break statement to exit from any loop in a nested loop.
for (int i = 0; i < 10; i++) {
abc:for (int j = 0; j < 10; j++) {
for (int k = 0; k < 10; k++) {
if (k == 1){
break abc;
}
}
}
}
The following code shows an example of exiting from the innermost loop.
In other works,after executing the following code, you are at the outside of the loop of 'k' variables and still inside the loop of 'j' and 'i' variables.
for (int i = 0; i < 10; i++) {
for (int j = 0; j < 10; j++) {
for (int k = 0; k < 10; k++) {
if (k == 1){
break;
}
}
}
}
I needed to do a similar thing, but I chose not to use the enhanced for loop to do it.
int s = type.size();
for (int i = 0; i < s; i++) {
for (int j = 0; j < t.size(); j++) {
if (condition) {
// do stuff after which you want
// to completely break out of both loops
s = 0; // enables the _main_ loop to terminate
break;
}
}
}
I prefer to add an explicit "exit" to the loop tests. It makes it clear to
any casual reader that the loop may terminate early.
boolean earlyExit = false;
for(int i = 0 ; i < 10 && !earlyExit; i++) {
for(int j = 0 ; i < 10 && !earlyExit; j++) { earlyExit = true; }
}
Java 8 Stream solution:
List<Type> types1 = ...
List<Type> types2 = ...
types1.stream()
.flatMap(type1 -> types2.stream().map(type2 -> new Type[]{type1, type2}))
.filter(types -> /**some condition**/)
.findFirst()
.ifPresent(types -> /**do something**/);
Labeled break concept is used to break out nested loops in java, by using labeled break you can break nesting of loops at any position.
Example 1:
loop1:
for(int i= 0; i<6; i++){
for(int j=0; j<5; j++){
if(i==3)
break loop1;
}
}
suppose there are 3 loops and you want to terminate the loop3:
Example 2:
loop3:
for(int i= 0; i<6; i++){
loop2:
for(int k= 0; k<6; k++){
loop1:
for(int j=0; j<5; j++){
if(i==3)
break loop3;
}
}
}
Usually in such cases, it is coming in scope of more meaningful logic, let's say some searching or manipulating over some of the iterated 'for'-objects in question, so I usually use the functional approach:
public Object searching(Object[] types) { // Or manipulating
List<Object> typesReferences = new ArrayList<Object>();
List<Object> typesReferences2 = new ArrayList<Object>();
for (Object type : typesReferences) {
Object o = getByCriterion(typesReferences2, type);
if(o != null) return o;
}
return null;
}
private Object getByCriterion(List<Object> typesReferences2, Object criterion) {
for (Object typeReference : typesReferences2) {
if(typeReference.equals(criterion)) {
// here comes other complex or specific logic || typeReference.equals(new Object())
return typeReference;
}
}
return null;
}
Major cons:
roughly twice more lines
more consumption of computing cycles, meaning it is slower from algorithmic point-of-view
more typing work
The pros:
the higher ratio to separation of concerns because of functional granularity
the higher ratio of re-usability and control of
searching/manipulating logic without
the methods are not long, thus they are more compact and easier to comprehend
higher ratio of readability
So it is just handling the case via a different approach.
Basically a question to the author of this question: what do you consider of this approach?
You can break from all loops without using any label: and flags.
It's just tricky solution.
Here condition1 is the condition which is used to break from loop K and J.
And condition2 is the condition which is used to break from loop K , J and I.
For example:
public class BreakTesting {
public static void main(String[] args) {
for (int i = 0; i < 9; i++) {
for (int j = 0; j < 9; j++) {
for (int k = 0; k < 9; k++) {
if (condition1) {
System.out.println("Breaking from Loop K and J");
k = 9;
j = 9;
}
if (condition2) {
System.out.println("Breaking from Loop K, J and I");
k = 9;
j = 9;
i = 9;
}
}
}
}
System.out.println("End of I , J , K");
}
}
Demo
public static void main(String[] args) {
outer:
while (true) {
while (true) {
break outer;
}
}
}
Best and Easy Method..
outerloop:
for(int i=0; i<10; i++){
// here we can break Outer loop by
break outerloop;
innerloop:
for(int i=0; i<10; i++){
// here we can break innerloop by
break innerloop;
}
}
Use Labels.
INNER:for(int j = 0; j < numbers.length; j++) {
System.out.println("Even number: " + i + ", break from INNER label");
break INNER;
}
Refer to this article
It's fairly easy to use label, You can break the outer loop from inner loop using the label, Consider the example below,
public class Breaking{
public static void main(String[] args) {
outerscope:
for (int i=0; i < 5; i++) {
for (int j=0; j < 5; j++) {
if (condition) {
break outerscope;
}
}
}
}
}
Another approach is to use the breaking variable/flag to keep track of required break. consider the following example.
public class Breaking{
public static void main(String[] args) {
boolean isBreaking = false;
for (int i=0; i < 5; i++) {
for (int j=0; j < 5; j++) {
if (condition) {
isBreaking = true;
break;
}
}
if(isBreaking){
break;
}
}
}
}
However, I prefer using the first approach.
boolean broken = false; // declared outside of the loop for efficiency
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
broken = true;
break;
}
}
if (broken) {
break;
}
}
If it is inside some function why don't you just return it:
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
return value;
}
}
}
Rather unusual approach but in terms of code length (not performance) this is the easiest thing you could do:
for(int i = 0; i++; i < j) {
if(wanna exit) {
i = i + j; // if more nested, also add the
// maximum value for the other loops
}
}
Another one solution, mentioned without example (it actually works in prod code).
try {
for (Type type : types) {
for (Type t : types2) {
if (some condition #1) {
// Do something and break the loop.
throw new BreakLoopException();
}
}
}
}
catch (BreakLoopException e) {
// Do something on look breaking.
}
Of course BreakLoopException should be internal, private and accelerated with no-stack-trace:
private static class BreakLoopException extends Exception {
#Override
public StackTraceElement[] getStackTrace() {
return new StackTraceElement[0];
}
}
Demo for break, continue, and label:
Java keywords break and continue have a default value. It's the "nearest loop", and today, after a few years of using Java, I just got it!
It's seem used rare, but useful.
import org.junit.Test;
/**
* Created by cui on 17-5-4.
*/
public class BranchLabel {
#Test
public void test() {
System.out.println("testBreak");
testBreak();
System.out.println("testBreakLabel");
testBreakLabel();
System.out.println("testContinue");
testContinue();
System.out.println("testContinueLabel");
testContinueLabel();
}
/**
testBreak
a=0,b=0
a=0,b=1
a=1,b=0
a=1,b=1
a=2,b=0
a=2,b=1
a=3,b=0
a=3,b=1
a=4,b=0
a=4,b=1
*/
public void testBreak() {
for (int a = 0; a < 5; a++) {
for (int b = 0; b < 5; b++) {
if (b == 2) {
break;
}
System.out.println("a=" + a + ",b=" + b);
}
}
}
/**
testContinue
a=0,b=0
a=0,b=1
a=0,b=3
a=0,b=4
a=1,b=0
a=1,b=1
a=1,b=3
a=1,b=4
a=2,b=0
a=2,b=1
a=2,b=3
a=2,b=4
a=3,b=0
a=3,b=1
a=3,b=3
a=3,b=4
a=4,b=0
a=4,b=1
a=4,b=3
a=4,b=4
*/
public void testContinue() {
for (int a = 0; a < 5; a++) {
for (int b = 0; b < 5; b++) {
if (b == 2) {
continue;
}
System.out.println("a=" + a + ",b=" + b);
}
}
}
/**
testBreakLabel
a=0,b=0,c=0
a=0,b=0,c=1
* */
public void testBreakLabel() {
anyName:
for (int a = 0; a < 5; a++) {
for (int b = 0; b < 5; b++) {
for (int c = 0; c < 5; c++) {
if (c == 2) {
break anyName;
}
System.out.println("a=" + a + ",b=" + b + ",c=" + c);
}
}
}
}
/**
testContinueLabel
a=0,b=0,c=0
a=0,b=0,c=1
a=1,b=0,c=0
a=1,b=0,c=1
a=2,b=0,c=0
a=2,b=0,c=1
a=3,b=0,c=0
a=3,b=0,c=1
a=4,b=0,c=0
a=4,b=0,c=1
*/
public void testContinueLabel() {
anyName:
for (int a = 0; a < 5; a++) {
for (int b = 0; b < 5; b++) {
for (int c = 0; c < 5; c++) {
if (c == 2) {
continue anyName;
}
System.out.println("a=" + a + ",b=" + b + ",c=" + c);
}
}
}
}
}
for (int j = 0; j < 5; j++) //inner loop should be replaced with
for (int j = 0; j < 5 && !exitloops; j++).
Here, in this case complete nested loops should be exit if condition is True . But if we use exitloops only to the upper loop
for (int i = 0; i < 5 && !exitloops; i++) //upper loop
Then inner loop will continues, because there is no extra flag that notify this inner loop to exit.
Example : if i = 3 and j=2 then condition is false. But in next iteration of inner loop j=3 then condition (i*j) become 9 which is true but inner loop will be continue till j become 5.
So, it must use exitloops to the inner loops too.
boolean exitloops = false;
for (int i = 0; i < 5 && !exitloops; i++) { //here should exitloops as a Conditional Statement to get out from the loops if exitloops become true.
for (int j = 0; j < 5 && !exitloops; j++) { //here should also use exitloops as a Conditional Statement.
if (i * j > 6) {
exitloops = true;
System.out.println("Inner loop still Continues For i * j is => "+i*j);
break;
}
System.out.println(i*j);
}
}
Like #1800 INFORMATION suggestion, use the condition that breaks the inner loop as a condition on the outer loop:
boolean hasAccess = false;
for (int i = 0; i < x && hasAccess == false; i++){
for (int j = 0; j < y; j++){
if (condition == true){
hasAccess = true;
break;
}
}
}
Java does not have a goto feature like there is in C++. But still, goto is a reserved keyword in Java. They might implement it in the future. For your question, the answer is that there is something called label in Java to which you can apply a continue and break statement. Find the code below:
public static void main(String ...args) {
outerLoop: for(int i=0;i<10;i++) {
for(int j=10;j>0;j--) {
System.out.println(i+" "+j);
if(i==j) {
System.out.println("Condition Fulfilled");
break outerLoop;
}
}
}
System.out.println("Got out of the outer loop");
}
If it's a new implementation, you can try rewriting the logic as if-else_if-else statements.
while(keep_going) {
if(keep_going && condition_one_holds) {
// Code
}
if(keep_going && condition_two_holds) {
// Code
}
if(keep_going && condition_three_holds) {
// Code
}
if(keep_going && something_goes_really_bad) {
keep_going=false;
}
if(keep_going && condition_four_holds) {
// Code
}
if(keep_going && condition_five_holds) {
// Code
}
}
Otherwise you can try setting a flag when that special condition has occured and check for that flag in each of your loop-conditions.
something_bad_has_happened = false;
while(something is true && !something_bad_has_happened){
// Code, things happen
while(something else && !something_bad_has_happened){
// Lots of code, things happens
if(something happened){
-> Then control should be returned ->
something_bad_has_happened=true;
continue;
}
}
if(something_bad_has_happened) { // The things below will not be executed
continue;
}
// Other things may happen here as well, but they will not be executed
// once control is returned from the inner cycle.
}
HERE! So, while a simple break will not work, it can be made to work using continue.
If you are simply porting the logic from one programming language to Java and just want to get the thing working you can try using labels.
You just use label for breaking inner loops
public class Test {
public static void main(String[] args) {
outerloop:
for (int i=0; i < 5; i++) {
for (int j=0; j < 5; j++) {
if (i * j > 6) {
System.out.println("Breaking");
break outerloop;
}
System.out.println(i + " " + j);
}
}
System.out.println("Done");
}
}
You can do the following:
set a local variable to false
set that variable true in the first loop, when you want to break
then you can check in the outer loop, that whether the condition is set then break from the outer loop as well.
boolean isBreakNeeded = false;
for (int i = 0; i < some.length; i++) {
for (int j = 0; j < some.lengthasWell; j++) {
//want to set variable if (){
isBreakNeeded = true;
break;
}
if (isBreakNeeded) {
break; //will make you break from the outer loop as well
}
}
I was trying to solve a question in Leetcode, and one of the discussed solutions was the following:
public class Solve {
public static void main(String[] args) {
String haystack = "mississippi";
String needle = "issip";
System.out.println(strStr(haystack,needle)) ;
}
public static int strStr(String haystack, String needle) {
for (int i = 0; ; i++) {
for (int j = 0; ; j++) {
if (j == needle.length()) return i;
if (i + j == haystack.length()) return -1;
if (needle.charAt(j) != haystack.charAt(i + j)) break;
}
}
}
}
Shouldn't the compiler have thrown a "No return statement" error here?
for (int i = 0; ; i++) {
for (int j = 0; ; j++) {
if (j == needle.length()) return i;
if (i + j == haystack.length()) return -1;
if (needle.charAt(j) != haystack.charAt(i + j)) break;
}
}
Here both of the for loops are infinite loops. The break statement only breaks out of the inner for loop. Therefore there is no exit condition for the outer for loop except the return statements. There is no path for which the method cannot return a value so there is no reason for the compiler to complain.
this is because you don't specify corner values for loop counters.
if you add smth like i<N; or j<N; you would got compiler warning.
But till that it's the same as:
while (true) {
}
The first for loop is infinite for the compiler, we know it will return, but compiler has no reason to complain. Good question though.
Your both for loops are infinite, the second one breaks or returns someday anyway! but the first one even has no break, then Java knows the you never rich to the last line.
for (int i = 0; ; i++) {
//Your second loop which is capable of returning or breaking (the second one is not technically infinite.
}
I'm having trouble in getting the rest of the numbers after I sum up the first 3 elements. This is the question that it asks me: "Write a method that takes an array. return true if the sum of the first three elements in the array is less than the sum of the rest of the elements of the array."
Therefore 5 5 5 5 2 2 should be false. Since the first 3 numbers sum are greater than the sum of 5 2 2. My program returns true for this question and I would appreciate any help.
public static boolean sumThree(int [] myArray)
{
int sum = 0;
for(int i = 0; i < myArray.length; i++)
{
sum += myArray[i];
}
int sumof3E = myArray[0] + myArray[1] + myArray[2];
if(sum > sumof3E)
{
return true;
}
else if(sumof3E < sum)
{
return false;
}
else
{
return false;
}
}
You shouldn't include the first three elements of the array. Those have to be exclusive of the summation.
Change the for loop control variable to this:
for (int i = 3; i < myArray.length; i++) {
sum += myArray[i];
}
Also, you should remove the else if block from your code, because it's redundant (the first if statement checks for that condition):
else if(sumof3E < sum)
{
return false;
}
Alternatively, with the help of java 8 features, you can shorten your code into one line:
public static boolean sumThree(int [] myArray){
return Arrays.stream(myArray).limit(3).sum() < Arrays.stream(myArray).skip(3).sum();
}
note - with the alternative solution you won't get IndexOutOfBoundsException even if the array being passed in is empty.
There are two issues in your code:
1) You don't verify that the Array even has 3 elements before you index into it, which will potentially cause errors.
2) You're summing the entire array and comparing it to the sum of the first three elements... in your loop try initializing i = 3 in the loop initialization (assuming the array has at least 4 elements)
Pseudo code:
public static boolean sumThree(int [] myArray)
{
if (myArray.length < 4) { return false; }
var first = myArray[0] + myArray[1] + myArray[2];
var rest = 0;
for(int i = 3; i<myArray.length; i++) {
rest += myArray[i];
}
return first < rest;
}
the sum loop need to be altered to start from index 2 and else if is not required.
public static boolean sumThree(int[] myArray) {
int sum = 0;
for (int i = 3; i < myArray.length; i++) {
sum += myArray[i];
}
int sumof3E = myArray[0] + myArray[1] + myArray[2];
if (sum > sumof3E) {
return true;
}
else {
return false;
}
}
for clarity make a two loop then use the conditional operator or known as ternary operator for using thee if..else easily
int sum1=0;
int sum2=0;
for(int i=0;i<=2;++i)
{
sum1+=myArray[i];
}
for(int i=3;i<myArray.length;++i)
{
sum2+=myArray[i];
}
boolean myBool = (sum1>sum2)?false:true;
return myBool;
There is no need to keep going through the whole array at a time when first sum becomes less than sum of rest:
int sumf3 =0;
int sumRest=0;
for (int i = 0; i < myArray.length; i++)
{
if (i < 3){
sumf3 += myArray[i];
} else {
sumRest += myArray[i];
}
if(sumf3 < sumRest ){
return true;
}
}
return false;
P.S. and no need to check size of array before loop as well.
public class Prime
{
public static void main(String [] args)
{
int num = 3;
int counter = 1;
boolean flag = true;
while(counter < 10001)
{
for(int i = 2; i < num; i++)
{
if(num%i==0)
{
flag = false;
}
}
if(flag)
{
counter++;
}
num++;
}
System.out.println(num);
}
}
Whenever I run this code, no result is printed out. I'm assuming its because the code is inefficient, but I don't know what is wrong with this code.
Your problem is that you don't reset flag to true before the for loop; so once it is false, it remains false, so counter is never incremented, meaning the while loop guard never becomes false.
This is an example of why you should declare variables in the tightest possible scope (i.e. inside the while loop).
while(counter < 10001)
{
int flag = true;
for (...) {...}
if (flag) { counter++; }
// ...
}
It's also an example of why you should make sure your code is correct before you think about whether it is efficient. Had you debugged the code (or even just added in a few System.out.printlns), you could have found that it wasn't actually doing the right thing.
As mentioned by #AndyTurner you should declare flag = true; in while loop and also there is a slight error in your logic for finding the prime number.
You are incrementing the num after it is checked for prime. So, if your 3rd prime is 5, then it will print 6 as the answer. lly, if your 10001th prime is X, then it will print X + 1 as the answer.
I have posted the correct logic for your problem below. I hope it helps you.
public class Main
{
public static void main(String [] args)
{
int num = 2;
int counter = 1;
boolean flag = true;
while(counter < 10001)
{
flag = true;
num++;
for(int i = 2; i < num; i++)
{
if(num%i==0)
{
flag = false;
}
}
if(flag)
{
counter++;
}
}
System.out.println(num);
}
}
Its not printing cause its going in infinite loop as counter is not incremented once flag become false
public static void main(String [] args)
{
int num = 3;
int counter = 1;
boolean flag = true;
while(counter < 10001)
{
flag = true;
for(int i = 2; i < num; i++)
{
if(num%i==0)
{
flag = false;
}
}
if(flag)
{
counter++;
}
num++;
}
System.out.println(num);
}
Try this. hope it helped
I've got a nested loop construct like this:
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
// Do something and break...
break; // Breaks out of the inner loop
}
}
}
Now how can I break out of both loops? I've looked at similar questions, but none concerns Java specifically. I couldn't apply these solutions because most used gotos.
I don't want to put the inner loop in a different method.
I don't want to return the loops. When breaking I'm finished with the execution of the loop block.
Like other answerers, I'd definitely prefer to put the loops in a different method, at which point you can just return to stop iterating completely. This answer just shows how the requirements in the question can be met.
You can use break with a label for the outer loop. For example:
public class Test {
public static void main(String[] args) {
outerloop:
for (int i=0; i < 5; i++) {
for (int j=0; j < 5; j++) {
if (i * j > 6) {
System.out.println("Breaking");
break outerloop;
}
System.out.println(i + " " + j);
}
}
System.out.println("Done");
}
}
This prints:
0 0
0 1
0 2
0 3
0 4
1 0
1 1
1 2
1 3
1 4
2 0
2 1
2 2
2 3
Breaking
Done
Technically the correct answer is to label the outer loop. In practice if you want to exit at any point inside an inner loop then you would be better off externalizing the code into a method (a static method if needs be) and then call it.
That would pay off for readability.
The code would become something like that:
private static String search(...)
{
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
// Do something and break...
return search;
}
}
}
return null;
}
Matching the example for the accepted answer:
public class Test {
public static void main(String[] args) {
loop();
System.out.println("Done");
}
public static void loop() {
for (int i = 0; i < 5; i++) {
for (int j = 0; j < 5; j++) {
if (i * j > 6) {
System.out.println("Breaking");
return;
}
System.out.println(i + " " + j);
}
}
}
}
You can use a named block around the loops:
search: {
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
// Do something and break...
break search;
}
}
}
}
I never use labels. It seems like a bad practice to get into. Here's what I would do:
boolean finished = false;
for (int i = 0; i < 5 && !finished; i++) {
for (int j = 0; j < 5; j++) {
if (i * j > 6) {
finished = true;
break;
}
}
}
You can use labels:
label1:
for (int i = 0;;) {
for (int g = 0;;) {
break label1;
}
}
Use a function:
public void doSomething(List<Type> types, List<Type> types2){
for(Type t1 : types){
for (Type t : types2) {
if (some condition) {
// Do something and return...
return;
}
}
}
}
You can use a temporary variable:
boolean outerBreak = false;
for (Type type : types) {
if(outerBreak) break;
for (Type t : types2) {
if (some condition) {
// Do something and break...
outerBreak = true;
break; // Breaks out of the inner loop
}
}
}
Depending on your function, you can also exit/return from the inner loop:
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
// Do something and break...
return;
}
}
}
If you don't like breaks and gotos, you can use a "traditional" for loop instead the for-in, with an extra abort condition:
int a, b;
bool abort = false;
for (a = 0; a < 10 && !abort; a++) {
for (b = 0; b < 10 && !abort; b++) {
if (condition) {
doSomeThing();
abort = true;
}
}
}
Using 'break' keyword alone is not the appropriate way when you need to exit from more than one loops.
You can exit from immediate loop
No matter with how many loops your statement is surrounded with.
You can use 'break' with a label!
Here I've used the label "abc"
You can write your code as following, within any function in Java
This code shows how to exit from the most outer loop
abc:
for (int i = 0; i < 10; i++) {
for (int j = 0; j < 10; j++) {
for (int k = 0; k < 10; k++) {
if (k == 1){
break abc;
}
}
}
}
Also you can use break statement to exit from any loop in a nested loop.
for (int i = 0; i < 10; i++) {
abc:for (int j = 0; j < 10; j++) {
for (int k = 0; k < 10; k++) {
if (k == 1){
break abc;
}
}
}
}
The following code shows an example of exiting from the innermost loop.
In other works,after executing the following code, you are at the outside of the loop of 'k' variables and still inside the loop of 'j' and 'i' variables.
for (int i = 0; i < 10; i++) {
for (int j = 0; j < 10; j++) {
for (int k = 0; k < 10; k++) {
if (k == 1){
break;
}
}
}
}
I needed to do a similar thing, but I chose not to use the enhanced for loop to do it.
int s = type.size();
for (int i = 0; i < s; i++) {
for (int j = 0; j < t.size(); j++) {
if (condition) {
// do stuff after which you want
// to completely break out of both loops
s = 0; // enables the _main_ loop to terminate
break;
}
}
}
I prefer to add an explicit "exit" to the loop tests. It makes it clear to
any casual reader that the loop may terminate early.
boolean earlyExit = false;
for(int i = 0 ; i < 10 && !earlyExit; i++) {
for(int j = 0 ; i < 10 && !earlyExit; j++) { earlyExit = true; }
}
Java 8 Stream solution:
List<Type> types1 = ...
List<Type> types2 = ...
types1.stream()
.flatMap(type1 -> types2.stream().map(type2 -> new Type[]{type1, type2}))
.filter(types -> /**some condition**/)
.findFirst()
.ifPresent(types -> /**do something**/);
Labeled break concept is used to break out nested loops in java, by using labeled break you can break nesting of loops at any position.
Example 1:
loop1:
for(int i= 0; i<6; i++){
for(int j=0; j<5; j++){
if(i==3)
break loop1;
}
}
suppose there are 3 loops and you want to terminate the loop3:
Example 2:
loop3:
for(int i= 0; i<6; i++){
loop2:
for(int k= 0; k<6; k++){
loop1:
for(int j=0; j<5; j++){
if(i==3)
break loop3;
}
}
}
Usually in such cases, it is coming in scope of more meaningful logic, let's say some searching or manipulating over some of the iterated 'for'-objects in question, so I usually use the functional approach:
public Object searching(Object[] types) { // Or manipulating
List<Object> typesReferences = new ArrayList<Object>();
List<Object> typesReferences2 = new ArrayList<Object>();
for (Object type : typesReferences) {
Object o = getByCriterion(typesReferences2, type);
if(o != null) return o;
}
return null;
}
private Object getByCriterion(List<Object> typesReferences2, Object criterion) {
for (Object typeReference : typesReferences2) {
if(typeReference.equals(criterion)) {
// here comes other complex or specific logic || typeReference.equals(new Object())
return typeReference;
}
}
return null;
}
Major cons:
roughly twice more lines
more consumption of computing cycles, meaning it is slower from algorithmic point-of-view
more typing work
The pros:
the higher ratio to separation of concerns because of functional granularity
the higher ratio of re-usability and control of
searching/manipulating logic without
the methods are not long, thus they are more compact and easier to comprehend
higher ratio of readability
So it is just handling the case via a different approach.
Basically a question to the author of this question: what do you consider of this approach?
You can break from all loops without using any label: and flags.
It's just tricky solution.
Here condition1 is the condition which is used to break from loop K and J.
And condition2 is the condition which is used to break from loop K , J and I.
For example:
public class BreakTesting {
public static void main(String[] args) {
for (int i = 0; i < 9; i++) {
for (int j = 0; j < 9; j++) {
for (int k = 0; k < 9; k++) {
if (condition1) {
System.out.println("Breaking from Loop K and J");
k = 9;
j = 9;
}
if (condition2) {
System.out.println("Breaking from Loop K, J and I");
k = 9;
j = 9;
i = 9;
}
}
}
}
System.out.println("End of I , J , K");
}
}
Demo
public static void main(String[] args) {
outer:
while (true) {
while (true) {
break outer;
}
}
}
Best and Easy Method..
outerloop:
for(int i=0; i<10; i++){
// here we can break Outer loop by
break outerloop;
innerloop:
for(int i=0; i<10; i++){
// here we can break innerloop by
break innerloop;
}
}
Use Labels.
INNER:for(int j = 0; j < numbers.length; j++) {
System.out.println("Even number: " + i + ", break from INNER label");
break INNER;
}
Refer to this article
It's fairly easy to use label, You can break the outer loop from inner loop using the label, Consider the example below,
public class Breaking{
public static void main(String[] args) {
outerscope:
for (int i=0; i < 5; i++) {
for (int j=0; j < 5; j++) {
if (condition) {
break outerscope;
}
}
}
}
}
Another approach is to use the breaking variable/flag to keep track of required break. consider the following example.
public class Breaking{
public static void main(String[] args) {
boolean isBreaking = false;
for (int i=0; i < 5; i++) {
for (int j=0; j < 5; j++) {
if (condition) {
isBreaking = true;
break;
}
}
if(isBreaking){
break;
}
}
}
}
However, I prefer using the first approach.
boolean broken = false; // declared outside of the loop for efficiency
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
broken = true;
break;
}
}
if (broken) {
break;
}
}
If it is inside some function why don't you just return it:
for (Type type : types) {
for (Type t : types2) {
if (some condition) {
return value;
}
}
}
Rather unusual approach but in terms of code length (not performance) this is the easiest thing you could do:
for(int i = 0; i++; i < j) {
if(wanna exit) {
i = i + j; // if more nested, also add the
// maximum value for the other loops
}
}
Another one solution, mentioned without example (it actually works in prod code).
try {
for (Type type : types) {
for (Type t : types2) {
if (some condition #1) {
// Do something and break the loop.
throw new BreakLoopException();
}
}
}
}
catch (BreakLoopException e) {
// Do something on look breaking.
}
Of course BreakLoopException should be internal, private and accelerated with no-stack-trace:
private static class BreakLoopException extends Exception {
#Override
public StackTraceElement[] getStackTrace() {
return new StackTraceElement[0];
}
}
Demo for break, continue, and label:
Java keywords break and continue have a default value. It's the "nearest loop", and today, after a few years of using Java, I just got it!
It's seem used rare, but useful.
import org.junit.Test;
/**
* Created by cui on 17-5-4.
*/
public class BranchLabel {
#Test
public void test() {
System.out.println("testBreak");
testBreak();
System.out.println("testBreakLabel");
testBreakLabel();
System.out.println("testContinue");
testContinue();
System.out.println("testContinueLabel");
testContinueLabel();
}
/**
testBreak
a=0,b=0
a=0,b=1
a=1,b=0
a=1,b=1
a=2,b=0
a=2,b=1
a=3,b=0
a=3,b=1
a=4,b=0
a=4,b=1
*/
public void testBreak() {
for (int a = 0; a < 5; a++) {
for (int b = 0; b < 5; b++) {
if (b == 2) {
break;
}
System.out.println("a=" + a + ",b=" + b);
}
}
}
/**
testContinue
a=0,b=0
a=0,b=1
a=0,b=3
a=0,b=4
a=1,b=0
a=1,b=1
a=1,b=3
a=1,b=4
a=2,b=0
a=2,b=1
a=2,b=3
a=2,b=4
a=3,b=0
a=3,b=1
a=3,b=3
a=3,b=4
a=4,b=0
a=4,b=1
a=4,b=3
a=4,b=4
*/
public void testContinue() {
for (int a = 0; a < 5; a++) {
for (int b = 0; b < 5; b++) {
if (b == 2) {
continue;
}
System.out.println("a=" + a + ",b=" + b);
}
}
}
/**
testBreakLabel
a=0,b=0,c=0
a=0,b=0,c=1
* */
public void testBreakLabel() {
anyName:
for (int a = 0; a < 5; a++) {
for (int b = 0; b < 5; b++) {
for (int c = 0; c < 5; c++) {
if (c == 2) {
break anyName;
}
System.out.println("a=" + a + ",b=" + b + ",c=" + c);
}
}
}
}
/**
testContinueLabel
a=0,b=0,c=0
a=0,b=0,c=1
a=1,b=0,c=0
a=1,b=0,c=1
a=2,b=0,c=0
a=2,b=0,c=1
a=3,b=0,c=0
a=3,b=0,c=1
a=4,b=0,c=0
a=4,b=0,c=1
*/
public void testContinueLabel() {
anyName:
for (int a = 0; a < 5; a++) {
for (int b = 0; b < 5; b++) {
for (int c = 0; c < 5; c++) {
if (c == 2) {
continue anyName;
}
System.out.println("a=" + a + ",b=" + b + ",c=" + c);
}
}
}
}
}
for (int j = 0; j < 5; j++) //inner loop should be replaced with
for (int j = 0; j < 5 && !exitloops; j++).
Here, in this case complete nested loops should be exit if condition is True . But if we use exitloops only to the upper loop
for (int i = 0; i < 5 && !exitloops; i++) //upper loop
Then inner loop will continues, because there is no extra flag that notify this inner loop to exit.
Example : if i = 3 and j=2 then condition is false. But in next iteration of inner loop j=3 then condition (i*j) become 9 which is true but inner loop will be continue till j become 5.
So, it must use exitloops to the inner loops too.
boolean exitloops = false;
for (int i = 0; i < 5 && !exitloops; i++) { //here should exitloops as a Conditional Statement to get out from the loops if exitloops become true.
for (int j = 0; j < 5 && !exitloops; j++) { //here should also use exitloops as a Conditional Statement.
if (i * j > 6) {
exitloops = true;
System.out.println("Inner loop still Continues For i * j is => "+i*j);
break;
}
System.out.println(i*j);
}
}
Like #1800 INFORMATION suggestion, use the condition that breaks the inner loop as a condition on the outer loop:
boolean hasAccess = false;
for (int i = 0; i < x && hasAccess == false; i++){
for (int j = 0; j < y; j++){
if (condition == true){
hasAccess = true;
break;
}
}
}
Java does not have a goto feature like there is in C++. But still, goto is a reserved keyword in Java. They might implement it in the future. For your question, the answer is that there is something called label in Java to which you can apply a continue and break statement. Find the code below:
public static void main(String ...args) {
outerLoop: for(int i=0;i<10;i++) {
for(int j=10;j>0;j--) {
System.out.println(i+" "+j);
if(i==j) {
System.out.println("Condition Fulfilled");
break outerLoop;
}
}
}
System.out.println("Got out of the outer loop");
}
If it's a new implementation, you can try rewriting the logic as if-else_if-else statements.
while(keep_going) {
if(keep_going && condition_one_holds) {
// Code
}
if(keep_going && condition_two_holds) {
// Code
}
if(keep_going && condition_three_holds) {
// Code
}
if(keep_going && something_goes_really_bad) {
keep_going=false;
}
if(keep_going && condition_four_holds) {
// Code
}
if(keep_going && condition_five_holds) {
// Code
}
}
Otherwise you can try setting a flag when that special condition has occured and check for that flag in each of your loop-conditions.
something_bad_has_happened = false;
while(something is true && !something_bad_has_happened){
// Code, things happen
while(something else && !something_bad_has_happened){
// Lots of code, things happens
if(something happened){
-> Then control should be returned ->
something_bad_has_happened=true;
continue;
}
}
if(something_bad_has_happened) { // The things below will not be executed
continue;
}
// Other things may happen here as well, but they will not be executed
// once control is returned from the inner cycle.
}
HERE! So, while a simple break will not work, it can be made to work using continue.
If you are simply porting the logic from one programming language to Java and just want to get the thing working you can try using labels.
You just use label for breaking inner loops
public class Test {
public static void main(String[] args) {
outerloop:
for (int i=0; i < 5; i++) {
for (int j=0; j < 5; j++) {
if (i * j > 6) {
System.out.println("Breaking");
break outerloop;
}
System.out.println(i + " " + j);
}
}
System.out.println("Done");
}
}
You can do the following:
set a local variable to false
set that variable true in the first loop, when you want to break
then you can check in the outer loop, that whether the condition is set then break from the outer loop as well.
boolean isBreakNeeded = false;
for (int i = 0; i < some.length; i++) {
for (int j = 0; j < some.lengthasWell; j++) {
//want to set variable if (){
isBreakNeeded = true;
break;
}
if (isBreakNeeded) {
break; //will make you break from the outer loop as well
}
}