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KwickClips Java

Java: 196 short revision clips (page 3)

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

Reel showing the three ways to declare, create and initialise an array.What does new int[5] put in the boxes?41 secReel showing a loop using m.length to read input into every box.Why not write i < 5?40 secReel showing one loop computing sum, maximum and minimum of an array.Why start max and min at m[0]?39 secReel table showing a pointer moving through an array until the key matches.Does linear search need a sorted array?41 secReel showing the mid calculation and the low and high moves of binary search.How can 1000 items be searched in about 10 steps?40 secReel comparing linear and binary search on sorting need, method and speed.Which search suits a small unsorted list?40 secReel showing a search loop that flips a result message on a match.What does the exam answer print?40 secReel tracing bubble sort passes on the array 5 1 4 2.Why is it called bubble sort?40 secReel tracing selection sort passes with the smallest value chosen each time.Can a sort swap only once per pass?39 secReel showing the shift and insert steps of insertion sort.What is insertion sort like?37 secReel comparing the main idea of bubble, selection and insertion sort.Which sort makes the fewest swaps?40 secReel showing a 3 by 3 grid with row and column indexes.Why does a 2D array need two indexes?44 secReel showing nested loops printing a matrix row by row.Why does my matrix print on one long line?41 secReel matching each matrix sum with its loop order.What changes between row sums and column sums?43 secReel showing a 2 by 3 matrix beside its 3 by 2 transpose.What is a transpose?38 secReel showing an empty Student class extending Person and inheriting its method.What does extends do?39 secReel showing super() calling a parent constructor and super.info() calling a parent method.What are the two jobs of super?39 secReel table of access modifiers and whether a child class can use each.Why can my child class not see a field?41 secReel showing Crow overriding the cry method of Bird.Bird b = new Crow(); what does b.cry() print?41 secReel listing inheritance types and whether Java classes allow each.Can a class have two parents?40 secReel showing an abstract Shape class with a child square writing area().Why does new Shape() fail?43 secReel showing an interface Pay implemented by a Upi class.What is an interface?41 secReel showing a Bird variable holding a Crow and calling the overridden method.Whose method runs: the variable's or the object's?43 secReel listing Object class methods toString, equals and getClass.Who is the parent of a class with no extends?42 secReel comparing checked and unchecked exceptions on when they are found and whether handling is required.Why will my file program not compile?42 secReel showing try, catch and finally around a divide by zero.Can a program survive 10 / 0?43 secReel comparing throw and throws on job, position and what follows each.Which one needs an object?40 secReel showing a LowBal class extending Exception with a message constructor.How do you make your own exception?41 secTable: variable gets lost, file on disk is still there.Why is variable data lost?41 secPython code writing Riya 91 to m.txt and printing f.read() with output Riya 91.What does w mode do to old text?40 secTable: r, w give characters for .txt files; rb, wb give bytes for photos and PDF.Which mode gives raw bytes?43 secPython try block opening old.txt with except OSError printing No file yet.Why does except OSError catch a missing file?38 secReel tracing the call stack of fact(3) pushing and popping frames.Where do waiting calls go?44 secReel labelling the base case and recursive case of a factorial method.Why does my recursion crash with StackOverflowError?41 secReel table of four recursion programs with their base and recursive cases.What is the base case of GCD?45 secReel showing a recursive string reverse using substring and charAt.Can you reverse a word without a loop?41 secReel tracing push, peek and pop on a stack.Which plate comes off a pile first?44 secReel tracing insert and delete on a queue.Who is served first in a ticket line?43 secReel showing the circular queue wrap formula and the deque idea.Why does my queue say full when cells are empty?40 secReel showing a stack class with an array, top index, push and pop.What does top = -1 mean?42 secReel showing nodes with data and links ending at null.What does a node hold?43 secReel showing the correct order of insertion and deletion at the start of a list.Why did my whole list vanish?41 secReel showing a traversal loop moving a pointer until null.How do you visit every node without an index?43 secReel comparing array and linked list on size, access and insertion.Which gives faster access to item k?43 secA table of tree terms: root and leaf, degree, level and depth, and height.What is the degree of a node?43 secA table comparing pre, in and post order rules with outputs 50 30 70, 30 50 70 and 30 70 50.Which traversal prints the root last?43 secA search trace table: at 50 go left, at 30 go right, at 40 found.In a binary search tree, which side holds smaller values?41 secA quiz table asking for the leaves, the degree of node 30 and the height, with answers 20 and 70, 1, and 2.Which nodes are the leaves here?43 sec
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