If you want to read data from a network socket until a character sequence is found, you first need to read the data and then check the data for the escape sequence.
do
{
// read data
} while ( /* data is not escape sequence */ );
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If you want to read data from a network socket until a character sequence is found, you first need to read the data and then check the data for the escape sequence.
do
{
// read data
} while ( /* data is not escape sequence */ );
The while statement continually executes a block of statements while a particular condition is true
while (expression) {
statement(s)
}
do-while evaluates its expression at the bottom of the loop, and therefore, the statements within the do block are always executed at least once.
do {
statement(s)
} while (expression);
Now will talk about functional difference,
while-loops consist of a conditional branch instructions such as if_icmpge or if_icmplt and a goto statement. The conditional instruction branches the execution to the instruction immediately after the loop and therefore terminates the loop if the condition is not met. The final instruction in the loop is a goto that branches the byte code back to the beginning of the loop ensuring the byte code keeps looping until the conditional branch is met.
A Do-while-loops are also very similar to for-loops and while-loops except that they do not require the goto instruction as the conditional branch is the last instruction and is be used to loop back to the beginning
A do-while loop always runs the loop body at least once - it skips the initial condition check. Since it skips first check, one branch will be less and one less condition to be evaluated.
By using do-while you may gain performance if the expression/condition is complex, since it is ensured to loop atleast once. In that casedo-while could call for performance gain
Very Impressive findings here, http://blog.jamesdbloom.com/JavaCodeToByteCode_PartOne.html#while_loop
- First to me Iterating and Looping are 2 different things.
Eg: Increment a variable till 5 is Looping.
int count = 0;
for (int i=0 ; i<5 ; i++){
count = count + 1;
}
Eg: Iterate over the Array to print out its values, is about Iteration
int[] arr = {5,10,15,20,25};
for (int i=0 ; i<arr.length ; i++){
System.out.println(arr[i]);
}
Now about all the Loops:
- Its always better to use For-Loop when you know the exact nos of time you gonna Loop, and if you are not sure of it go for While-Loop. Yes out there many geniuses can say that it can be done gracefully with both of them and i don't deny with them...but these are few things which makes me execute my program flawlessly...
For Loop :
int sum = 0;
for (int i = 1; i <= 100; i++) {
sum += i;
}
System.out.println("The sum is " + sum);
The Difference between While and Do-While is as Follows :
- While is a Entry Control Loop, Condition is checked in the Beginning before entering the loop.
- Do-While is a Exit Control Loop, Atleast once the block is always executed then the Condition is checked.
While Loop :
int sum = 0;
int i = 0; // i is 0 Here
while (i<100) {
sum += i;
i++;
}
System.out.println("The sum is " + sum);
do-While :
int sum = 0;
int i = 0; // i is 0 Here
do{
sum += i;
i++
}while(i < 100; );
System.out.println("The sum is " + sum);
From Java 5 we also have For-Each Loop to iterate over the Collections, even its handy with Arrays.
ArrayList<String> arr = new ArrayList<String>();
arr.add("Vivek");
arr.add("Is");
arr.add("Good");
arr.add("Boy");
for (String str : arr){ // str represents the value in each index of arr
System.out.println(str);
}
Your for loop looks good.
A possible while loop to accomplish the same thing:
int sum = 0;
int i = 1;
while (i <= 100) {
sum += i;
i++;
}
System.out.println("The sum is " + sum);
A possible do while loop to accomplish the same thing:
int sum = 0;
int i = 1;
do {
sum += i;
i++;
} while (i <= 100);
System.out.println("The sum is " + sum);
The difference between the while and the do while is that, with the do while, at least one iteration is sure to occur.
Is there ever a situation where you must use a
do whileloop?
No: every do-while loop can be written as a while-loop by running the body once before the loop begins. However, there are certainly cases where it makes more sense to use the do-while construct (i.e. if you always want the loop to iterate at least once), which is why it exists in the first place.
Is it an accepted practice?
If you use it appropriately, then yes absolutely.
It seems like it is equivalent to a plain
whileloop except that its first iteration happens before checking the conditional, if that is even true.
That's right. You can read more about do-while in its tutorial.
This example maybe help you be clearer:
int i = 3;
System.out.print("while: ");
while (--i > 0){
System.out.print("x");
}
System.out.print("\ndo-while: ");
int j = 3;
do
{
System.out.print("x");
}while (--j > 0);
This prints
while: xx
do-while: xxx
Because when you type a and hit Enter, then the in.read() method returns three characters - 'a', the character for carriage return \r and the character for line break ('\n'). (Note that the combination \r\n is considered as line-break under Windows).
Your program will have significantly different behavior if you run it under Linux or OSX, because line-breaking character(s) is specific to the OS you're running the program on. Under Linux, it will be \n, under OS X-9 it will be \r, for example.
As a work-around, you can read the whole line (by using a Scanner) and trim it, which will omit the line-breaking character (disregarding the OS type):
public static void main (String args[]) throws java.io.IOException {
String line;
Scanner sc = new Scanner(System.in);
do {
System.out.println("Please a key followed by ENTER:");
line = sc.readLine().trim();
} while (!"q".equals(line));
}
I assume what gets read as input is containing your ENTER keypress. Since you are on Windows, this includes the CRFL line ending.
Thus, each time you entered your char, you actually input 3 chars. For your first input:
- a
- CR
- LF
Try reading a full line via a BufferedReader and run a whitespace trim on that, or just evaluate its first char.