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As you saw when working with switch statements, a break statement transfers the flow of control out to the enclosing statement. The same holds true for a break statement that appears inside of a while, do/while, or for loop, as it will end the loop early, as shown in Figure 3.9.

FIGURE 3.9 The structure of a break statement

Notice in Figure 3.9 that the break statement can take an optional label parameter. Without a label parameter, the break statement will terminate the nearest inner loop it is currently in the process of executing. The optional label parameter allows us to break out of a higher-level outer loop. In the following example, we search for the first (x,y) array index position of a number within an unsorted two-dimensional array:

public class FindInMatrix { public static void main(String[] args) { int[][] list = {{1,13},{5,2},{2,2}}; int searchValue = 2; int positionX = -1; int positionY = -1; PARENT_LOOP: for(int i=0; i<list.length; i++) { for(int j=0; j<list[i].length; j++) { if(list[i][j]==searchValue) { positionX = i; positionY = j; break PARENT_LOOP; } } } if(positionX==-1 || positionY==-1) { System.out.println("Value "+searchValue+" not found"); } else { System.out.println("Value "+searchValue+" found at: " + "("+positionX+","+positionY+")"); } } }

When executed, this code will output the following:

Value 2 found at: (1,1)

In particular, take a look at the statement break PARENT_LOOP. This statement will break out of the entire loop structure as soon as the first matching value is found. Now, imagine what would happen if we replaced the body of the inner loop with the following:

if(list[i][j]==searchValue) { positionX = i; positionY = j; break; }

How would this change our flow, and would the output change? Instead of exiting when the first matching value is found, the program would now only exit the inner loop when the condition was met. In other words, the structure would find the first matching value of the last inner loop to contain the value, resulting in the following output:

Value 2 found at: (2,0)

Finally, what if we removed the break altogether?

if(list[i][j]==searchValue) { positionX = i; positionY = j; }

In this case, the code would search for the last value in the entire structure that had the matching value. The output would look like this:

Value 2 found at: (2,1)

You can see from this example that using a label on a break statement in a nested loop, or not using the break statement at all, can cause the loop structure to behave quite differently.