Which is better Jan 14 2019 Which is better Assume s1 and s2 are Strings A if s1 s2 B if s1 equals s2 2 Answer B s1 s2 tests whether s1 and s2 reference the same string s1 equals s2 tests whether they reference equal strings String s1 ABC String s2 s1 String s3 ABC String s4 AB C All these strings are equal but s4 is in a different memory location than the others so the test yields false 3 Which is better Assume s1 is a String A if s1 equals OK B if OK equals s1 4 Answer B s1 equals OK sends a message to s1 asking if it is equal to OK OK equals s1 sends a message to OK asking if it is equal to s1 This is legal because OK is a String If s1 is null then s1 equals OK gives a NullPointerException OK equals s1 gives false 5 Which is best Assume int numbers new int 100 A B C D for int i 0 i 100 i numbers i i for int i 0 i 99 i numbers i i for int i 0 i ARRAY SIZE i numbers i i for int i 0 i numbers length i numbers i i 6 Answer D D is best for int i 0 i numbers length i C is OK for int i 0 i ARRAY SIZE i Changing ARRAY SIZE will fix this loop if array size is changed B is poor for int i 0 i 100 i numbers length changes automatically if array size is changed Uses a magic number Must track down and change each occurrence if array size is changed A is worst for int i 0 i 99 i This has all the same problems as B B is more traditional and therefore less surprising The array size is 100 not 99 so it s more obvious where the number came from You have to do some arithmetic to get 99 If you change the array size a search for 100 won t find the loop that uses 99 7 Which is better Assume finished is a boolean variable A if finished true B if finished 8 Answer B finished true is redundant If finished is true then finished true will be true If finished is false then finished true will be false The extra words don t gain you anything finished true might seem more readable to a beginner but you quickly learn to read the shorter form Brevity in programming as in writing is a virtue You can avoid the possible mistake of saying if finished true 9 Which is better Assume foo bar and larger are integers A B if foo bar larger foo else larger bar larger foo bar foo bar 10 Answer neither For each of these you have to look at the code carefully to make sure it is correct larger Math max foo bar is easier to read and more obviously correct 11 Which is better A String s Hello B String s new String Hello 12 Answer A Hello is special syntax to implicitly construct a string String s new String Hello actually constructs two strings Hello constructs the first string then it is given as a parameter to an explicit constructor which constructs the second string 13 Which is better Suppose p is a Panel with a BorderLayout and okButton is a Button A p add okButton BorderLayout NORTH B p add okButton North Note BorderLayout NORTH North 14 Answer A p add okButton BorderLayout NORTH is strongly recommended over the shorter form p add okButton North but why Answer The former gives better error detection If you type p add okButton north there is no error but it doesn t do what you want If you type p add okButton BorderLayout North you will get a syntax error because BorderLayout has no such variable as North 15 Which is best Suppose n is an int and s is a String A s Integer toString n B s String valueOf n C s new Integer n toString D s n 16 Answer D I prefer D s n because It s a common idiom therefore easily recognized It s short It works for any type 17 Which is best Assume n is an integer A B C if n 0 n 0 if n 0 n 0 if n 0 n 0 18 Answer C If later on you want to add a statement it s easy to make this mistake with B if n 0 System out println n was n n 0 You won t make this mistake with A or C With C using braces you don t have to change anything that s already there However A all on one line is often convenient 19 Which is better Assume n is an integer A B int factorial 1 for int i 2 i n i factorial n int factorial 1 int i for i 2 i n i factorial n 20 Answer A In most cases you don t care about the index of a for loop outside the loop You typically give it an initial value in the loop You typically already have its final value in some variable or by some simple computation If you don t need a variable you shouldn t have that variable It doesn t help anything and it might get in the way 21 Which is better A B int search int array int target for int i 0 i array length i if array i target return i return 1 int search int array int target throws NotFoundException for int i 0 i array length i if array i target return i return new NotFoundException 22 Answer A Exceptions should be used for exceptional cases not for normal program control In almost all cases not finding something in an array search is one of the expected outcomes 23 Which is better A B private void combinations int n int t throws InvalidArgumentException if t 0 t n throw new InvalidArgumentException private void combinations int n int t assert t 0 t n 24 Answer B The method is marked private so you the person writing this class will be the only one using this method If you call it incorrectly it s a bug not just an unexpected external event and should be fixed not tested for Besides using an assert statement is a lot less work 25 Which is better A B class Line public Point start public Point end public double length class Line public Point start public Point end public int length 26 Answer B Two main reasons The DRY principle says Don t repeat yourself The length variable makes the object vulnerable to inconsistent changes The length variable is a subtle kind of repetition its value is determined by the start and end points Whenever you have the same information represented in two places you have the extra requirement to keep them consistent If some external agency changed only the start or the end point the length variable would …
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