Java provides "built-in" classes for programmers to use. Some of them are here:
How to generate a random number between 0.0 - 1.0, 1.0 - 10.0, -10.0 - +10.0?
How to use absolute values, square root, or power of x?
Math.random() returns double, how to generate random integers for array indices?
Is "abc" an object? What's the difference between String x = "abc"; and String x = new String("abc");?
What will System.out.println("10" + "$") print out? What about System.out.println(10 + "$")?
How to compare two strings str1 and str2?
Wrapper classes: Integer and Double
How to create an object from a primitive type value of int or double?
How to convert an object back to an int or double value?
How to compare Integer or Double objects?
Object class (To be discussed later):
What are some common behaviors that ALL classes have?
Is Object class a class or an object?
When to override toString() and equals()? What is the hash code of an object?
How to use substring() and charAt() method of String class to swap any two characters in a string?
How to find first and last digit of any integer by turning the integer into a string?
How to convert an integer in decimal system to an integer in binary system or vice versa using Integer.parseInt() and Integer.toBinaryString()?
Barron's: #1-21 of Chapter 5 "Some Standard Classes"