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KwickClips Java

Java: 196 short revision clips (page 2)

One idea per clip, with the answer written out underneath. Each clip links back to the full Java lesson it came from.

Reel showing a switch on 2 without break falling through case 3 and default.Why did the switch print three things?42 secReel showing a menu switch with area and perimeter cases.How does a menu program work?41 secReel showing System.exit(0) stopping a program before the next print line.What stops the whole program?40 secReel table tracing counter i against the condition and what prints.Do you need 100 print lines for 1 to 100?44 secReel labelling the initialisation, condition and update of a for loop.What are the three parts of a for loop?42 secReel comparing while and do-while on when the condition is checked and the minimum runs.How can a loop run when the condition is false?40 secReel matching each situation with the loop to use.Which loop suits printing a table 1 to 10?43 secReel showing for(...); with a separate block that runs only once.Why did my loop add only once?41 secReel comparing the output of break and continue in the same loop.What does break print here?41 secReel showing a labelled outer loop exited by break outer.How do you exit two loops at once?42 secReel labelling for(;;), while(true) and for(...); as infinite or empty.Why is for(;;) infinite?44 secReel counting the iterations of a for loop stepping by 2.How many times does for (i=1; i<=9; i+=2) run?44 secReel tracing a 3 by 3 nested loop row by row.How many prints does a 3 by 3 nested loop make?43 secReel showing a star triangle with the inner loop bounded by i.Why does each row get one more star?40 secReel listing prime, perfect, Armstrong and palindrome numbers with examples.Why is 153 special?41 secReel trace table of i, the j values and the row printed.What is a dry run?42 secReel explaining reuse and modularity as the reasons for methods.Why use a method?42 secReel labelling a method header and naming its signature.Is the return type part of the signature?41 secReel showing a bill method being called with two arguments.What happens if you only define a method?37 secReel showing an int passed as a copy so the caller's value is unchanged.Why did marks not change?40 secReel comparing a pure method with an impure one that changes a balance.What makes a method impure?39 secReel showing three overloaded area methods with different parameter lists.Can two methods have the same name?42 secReel showing calc(5) choosing the long overload over the double one.Which version runs for calc(5) when only long and double exist?42 secReel comparing overloading and overriding on class, parameters and timing.What is the main difference?41 secReel showing two overloaded vol methods for a cube and a cuboid.How do you find cube and cuboid volume with one name?36 secReel showing a simple Stu constructor setting marks to 0.Who gives a new object its starting values?38 secReel showing a parameterised constructor removing the hidden default.Why does new Stu() give an error?41 secReel showing two Box constructors for a square and a rectangle.Can a class have two constructors?39 secReel showing this.name = name storing a constructor parameter into the field.Why does the field print null?40 secReel comparing constructor and method on name, return type and how each runs.What is the first difference?39 secReel showing one shared static box beside separate instance boxes per object.How many copies does a static variable have?40 secReel showing a static cube method called as Calc.cube(3).Can you call a method without an object?37 secReel showing a static method failing to use an instance variable.Why does this not compile?40 secReel table checking school name, count and marks against the static test.Should marks be static?44 secReel table of private, default, protected and public with where each is visible.What do you get if you write no access keyword?41 secReel showing a private balance with a getter and a checking setter.How do you stop a negative balance?38 secReel table of local, argument, instance and static variables and how long each lives.Why does my loop variable vanish?41 secReel listing three exam visibility rules for private, protected and local variables.Can a subclass use a private member?44 secReel table of primitives with their wrapper class names.Is an int an object in Java?42 secReel showing autoboxing into an Integer and unboxing during addition.Does Integer obj = 45 compile?42 secReel showing Integer.parseInt fixing a text plus number addition.Why is "25" + 5 equal to 255?40 secReel table of Character test methods with example characters.How do you check if a character is a digit?43 secReel showing toUpperCase() lost, then stored back into s.Why did my string stay in small letters?39 secReel table of length, charAt, indexOf and substring results on banana.Where does indexing start?43 secReel comparing ==, equals and compareTo for two strings.Why is == false for two identical strings?42 secReel table of trim, replace, concat and toUpperCase results.How do you remove extra spaces a user typed?42 secReel building a reversed string and comparing it with equals.How do you check a palindrome?41 secReel showing an array as numbered boxes with index and value.Do forty students need forty variables?46 sec
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