I'm a fledgling programmer for the first year. This is a collection of personal notes that have been organized and published for review purposes. Please note that there is a high possibility that you are wrong.
int number; //Declare variable number of type int String str; //Declare a variable str of type String int list; //Declaration of array list of int type ArrayList<String> arrList; // ArrayList<String>Declare the variable arrList of the class
--Declare in the order of type variables
int number = 27; //Variable initialization (assigning a value for the first time) String str = "hello"; //String type initialization, string""Enclose with (double quotation marks) int list = new int //Creating an array List<String> arrList = new ArrayList<String>(); //Instantiation of ArrayList class
--If not initialized, the initial value is set to 0 for numeric types such as int and double, false for boolean type, and null for reference type. --Learn later what the instance is
final int NUMBER = 5;
--If final is added, it becomes a constant and an error occurs when trying to assign a value. --By convention, constants are often capitalized.
|long||Large number||64bit||-9223372036854775808 ～ 9223372036854775807|
|int||Normal number||32bit||-2147483648 ～ 2147483647|
|shot||Small number||16bit||-32768 ～ 32767|
|byte||Very small number||8bit||-128 ～ 127|
|float||Decimal numbers with relatively low precision||32bit||(-)1.79769313486231570E+388 (15-digit precision)|
|boolean||True or false||16bit||true or false|
|char||1 Unicode character||1bit||\u0000 ～ \uFFFF|
--Typical example is String class, reference type if not primitive type
System.out.print((int)3.2); //The result is 3
--Forcibly perform type conversion by explicitly performing type conversion --It seems that it is not used much because data is lost.
--String → Numerical value
--Numeric value → character string
I wrote a lot, but I thought it would be better to see Java Road. So let's look at this (round throw).