Hot cup of Java sir?

Like IF statements loops can be nested. Actually most things in Java can be nested! Let us consider a classic algorithim called bubble sort -

for(int a=0; a<numbers.length; a++){
- for(int b=0; b<numbers.length - (a+1); b++){
  - if(numbers[b] > numbers[b + 1] ){
    - int temp = numbers[b];
    - numbers[b] = numbers[b+1];
    - numbers[b+1] = temp;
  - }
- }
}

This code will sort an array of numbers into ascending order. It does it by looping a loop! Look at the code below and the output. Notice that the inner loop will run through before the outer loop increments -

int a=0;
int b=0;
for(System.out.println("A start"); a<3; System.out.println("A inc to " + a)){
1. System.out.println("A run");
2. b=0;
3. for(System.out.println("B start"); b<3; System.out.println("B inc to " + b)){
  1. System.out.println("B run");
  2. b = b + 1;
4. }
5. a = a + 1;
}

A start
A run
B start
B run
B inc to 1
B run
B inc to 2
B run
B inc to 3
A inc to 1
A run
B start
B run
B inc to 1
B run
B inc to 2
B run
B inc to 3
A inc to 2
A run
B start
B run
B inc to 1
B run
B inc to 2
B run
B inc to 3
A inc to 3

Notice that "B start" is called 3 times (once per itteration of the outer loop) while "A start" is only called once. The inner most code block will run A * B times where A and B are the amount of itterations of the inner or outer loop.

Going back to bubble sort, the inner code will run aproximatly N^2 where N is the size of the array.

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