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(base) MAC:Tue Oct 12:09:20:~> jshell
|  Welcome to JShell -- Version 15.0.1
|  For an introduction type: /help intro

jshell> ArrayList<String> al = new ArrayList<>();
al ==> []

jshell> al.add(new ArrayList<String>())
|  Error:
|  incompatible types: java.util.ArrayList<java.lang.String> cannot be converted to java.lang.String
|  al.add(new ArrayList<String>())
|         ^---------------------^

jshell> al.add("hello")
$2 ==> true

jshell> al.add("goodbye")
$3 ==> true

jshell> ArrayList<int> nums = new ArrayList<int>();
|  Error:
|  unexpected type
|    required: reference
|    found:    int
|  ArrayList<int> nums = new ArrayList<int>();
|            ^-^
|  Error:
|  unexpected type
|    required: reference
|    found:    int
|  ArrayList<int> nums = new ArrayList<int>();
|                                      ^-^

jshell> ArrayList<Integer> = new ArrayList<>();
|  Error:
|  illegal start of expression
|  ArrayList<Integer> = new ArrayList<>();
|                     ^
|  Error:
|  cannot find symbol
|    symbol:   variable ArrayList
|  ArrayList<Integer> = new ArrayList<>();
|  ^-------^
|  Error:
|  cannot find symbol
|    symbol:   variable Integer
|  ArrayList<Integer> = new ArrayList<>();
|            ^-----^

jshell> ArrayList<Integer> nums = new ArrayList<>();
nums ==> []

jshell> Integer.MAX_VALUE
$5 ==> 2147483647

jshell> Integer.MIN_VALUE
$6 ==> -2147483648

jshell> Integer i = 4;
i ==> 4

jshell> //this is called autoboxing

jshell> int p = 4;
p ==> 4

jshell> p.getClass()
|  Error:
|  int cannot be dereferenced
|  p.getClass()
|  ^--------^

jshell> i.getClass()
$9 ==> class java.lang.Integer

jshell> int q = i;
q ==> 4

jshell> q
q ==> 4

jshell> //autounboxing

jshell> Integer.sgn(q)
|  Error:
|  cannot find symbol
|    symbol:   method sgn(int)
|  Integer.sgn(q)
|  ^---------^

jshell> Integer.signum(q)
$12 ==> 1

jshell> Integer.signum(-3)
$13 ==> -1

jshell> Integer.signum(0)
$14 ==> 0

jshell> Integer.toString(42)
$15 ==> "42"

jshell> Integer.parseInt("3214")
$16 ==> 3214

jshell> Integer.parseInt("cows")
|  Exception java.lang.NumberFormatException: For input string: "cows"
|        at NumberFormatException.forInputString (NumberFormatException.java:68)
|        at Integer.parseInt (Integer.java:652)
|        at Integer.parseInt (Integer.java:770)
|        at (#17:1)

jshell> 

jshell> Double.parseDouble("6.02e23")
$18 ==> 6.02E23

jshell> Boolean.parseBoolean("true")
$19 ==> true

jshell> /imports
|    import java.io.*
|    import java.math.*
|    import java.net.*
|    import java.nio.file.*
|    import java.util.*
|    import java.util.concurrent.*
|    import java.util.function.*
|    import java.util.prefs.*
|    import java.util.regex.*
|    import java.util.stream.*

jshell>