Ordering of Statements in Methods
Consider the following two methods:
public void count1(int x) {
if (X <= 0) {
System.out.println(x);
} else {
System.out.println(x);
count1(x-1);
}
}
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public void count2(int x) {
if (X <= 0) {
System.out.println(x);
} else {
count2(x-1);
System.out.println(x);
}
}
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- Do they calculate the same values?
- Do they do the calculations in the same way?
- Do they print the same results?
Execution
Executing with x=4:
Entering count1(4)
4
Entering count1(3)
3
Entering count1(2)
2
Entering count1(1)
1
Entering count1(0)
0
Exiting count1(0)
Exiting count1(1)
Exiting count1(2)
Exiting count1(3)
Exiting count1(4)
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Entering count2(4)
Entering count2(3)
Entering count2(2)
Entering count2(1)
Entering count2(0)
0
Exiting count2(0)
1
Exiting count2(1)
2
Exiting count2(2)
3
Exiting count2(3)
4
Exiting count2(4)
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- count1 has no deferred operations -- when the recursive call is completed, no further calculations must be done.
- This is tail recursive and an interative process.
- Some languages will optimize its implementation eliminating the recursion.
- count2 has a deferred operation -- the print operation is deferred until after the recursive call.
- This is a recursive process and cannot be optimized.
- Note that both are implemented using recursion.
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