The Java Language: break/continue

The Java break statement and its friend continue can also be used to cut short a loop or conditional statement by jumping out of it. A break causes Java to stop the current block statement and resume execution after it. In the following example, the while loop goes on endlessly until the condition() method returns true, triggering a break statement that stops the loop and proceeds at the point marked “after while.”

 while( true ) {  
 if ( condition() )  
 break;  
 }  
 // after while  

A continue statement causes for and while loops to move on to their next iteration by returning to the point where they check their condition. The following example prints the numbers 0 through 99, skipping number 33.

 for( int i=0; i < 100; i++ ) {  
 if ( i == 33 )  
 continue;  
 System.out.println( i );  
 }  

The break and continue statements look like those in the C language, but Java’s forms have the additional ability to take a label as an argument and jump out multiple levels to the scope of the labeled point in the code. This usage is not very common in day-today Java coding, but may be important in special cases. Here is an outline:

labelOne:
 while ( condition ) {  
 ...  
 labelTwo:  
 while ( condition ) {  
 ...  
 // break or continue point  
 }  
 // after labelTwo  
 }  
 // after labelOne  

Enclosing statements, such as code blocks, conditionals, and loops, can be labeled with identifiers like labelOne and labelTwo. In this example, a break or continue without argument at the indicated position has the same effect as the earlier examples. A break causes processing to resume at the point labeled “after labelTwo”; a continue immediately causes the labelTwo loop to return to its condition test. The statement break labelTwo at the indicated point has the same effect as an ordinary break, but break labelOne breaks both levels and resumes at the point labeled “after labelOne.” Similarly, continue labelTwo serves as a normal continue, but continue labelOne returns to the test of the labelOne loop. Multilevel break and continue statements remove the main justification for the evil goto statement in C/C++. There are a few Java statements we aren’t going to discuss right now. The try , catch, and finally statements are used in exception handling, as we’ll discuss later. The synchronized statement in Java is used to coordinate access to statements among multiple threads of execution; We will have a discussion of thread synchronization.