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KwickClips Java

Java: 196 short revision clips

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

Table comparing 7 / 2, 7 / 2.0 and 7 % 2 with their printed results.Why does 7 / 2 print 3?43 secJava class Box showing a constructor Box(int v) beside a method int area().Is a constructor a method?41 secTable comparing array length and m[0] with String length() and charAt(0).Which one needs brackets?40 secReel listing the four Class 11 Java topics most reused in Class 12 papers.Which Class 11 topics return in Class 12?45 secReel listing where Java runs: Android apps, servers, websites and school labs.Is Java still used?43 secReel showing source code compiled by javac into bytecode, then run by the JVM.What does javac produce?39 secReel showing JDK containing JRE containing JVM with each one's job.Which contains which?47 secReel listing the four BlueJ steps to compile and run a Hello class.What are the BlueJ steps?40 secReel showing the Java program skeleton: class, main method and statements.Why will my program not compile?41 secTable comparing add(bal, 200) outside the data with riya.add(200) inside an object.Where does the data live in procedure style?39 secTable: Phone with battery and charge, Student with marks and study.What is state?41 secTable with Abstraction: just tap Pay, and Encapsulation: PIN hidden.What does abstraction do?40 secBullet list: each class does one job, inheritance reuses code, fix one class not the app.How does OOP help with bugs?42 secTable: house plan gives many houses; Student class gives riya and aman.What is a class?41 secPython class Phone with a charge method setting self.battery = 100 and printing 100.What do data members hold?39 secPython code a = S(), b = a, b.name = "Aman", print(a.name) with output Aman.What does print(a.name) show after b.name = "Aman"?43 secPython code riya = Student(), riya.marks = 91, print(riya.marks) with output 91.What does riya.marks = 91 do?40 secPython code printing type(5) and type(Student()) with outputs class int and class __main__.Student.What does type(Student()) print?40 secReel splitting int marks = 90; into its five tokens.How many tokens are in int marks = 90;?43 secReel on Java keywords: fixed meanings, lowercase, and the unused goto and const.Can you name a variable int?43 secReel checking four Java names as valid or invalid with the reason.Is 2ndTerm a valid Java name?43 secReel listing six kinds of Java literal with examples.Is 010 equal to 10?41 secReel listing Java escape sequences and what each one prints.How do you print a double quote inside a String?43 secReel table of Java primitive type sizes in bytes.How big is a char in Java?44 secReel comparing primitive and reference variables on what they hold and whether they can be null.Is String a primitive type?41 secReel showing int total; failing to print until it is given a value.Why won't my program compile after int total;?37 secReel showing final int DAYS = 7; and the error when it is reassigned.What does final do?36 secReel table of Java default values for int, double, boolean and String fields.What does an int field with no value print?40 secReel showing int runs = 250 widened into double avg printing 250.0.Why does an int go into a double without a cast?41 secReel showing double price 99.99 cast to int giving 99.Where did the paise go?38 secReel table of promotion results for byte, int, long, float and double operands.Why does storing byte + byte in a byte fail?43 secReel comparing (double)7 / 2 with (double)(7/2) and their printed results.Why is (double)(7/2) only 3.0?41 secReel table of the four Java operator groups with examples.What is the difference between = and ==?43 secReel tracing a++ + ++a step by step with the value of a after each step.What is a++ + ++a when a is 5?42 secReel showing a ternary operator choosing Pass for marks of 68.Can an if-else fit on one line?39 secReel showing 6 and 3 in binary with the result of a bitwise AND.Why is 6 & 3 equal to 2?44 secReel evaluating 10 - 4 + 1 left to right with the precedence rule.Is 10 - 4 + 1 equal to 5 or 7?41 secReel table of three input ways with a code example each.What are the three ways to give data?40 secReel table of Scanner methods against what each reads from 45.5 Riya.Which method reads only one word?44 secReel showing an extra sc.nextLine() added after nextInt() to fix the empty name.Why does Java skip my name?41 secReel showing args[0], args[1] and args.length for java Greet Riya 15.Can you give input before the program starts?43 secReel table of Math.sqrt, cbrt, pow and abs with their results.Why 7.0 and not 7?43 secReel showing Math.max called twice to find the highest of three marks.Can Math.max take three numbers?43 secReel table of ceil, floor and round results for -4.5.Why is Math.round(-4.5) equal to -4?41 secReel building a dice roll from Math.random() with a multiply, cast and add.How do you roll a dice in Java?40 secReel mapping maths notation to Java expressions with explicit multiplication.Is 2ab valid Java?45 secReel showing an if-else-if ladder assigning grade A for marks of 75.Marks are exactly 75. Which grade prints?41 secReel showing a nested if checking age then an ID card.When is the inner if checked?40 sec
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