What is the difference between javascript and java

The difference between javascript and java

java is an object-oriented programming language launched by SUN;

javaScript is an object-based and event-driven interpretive language (scripting language) launched by Netscape that can be embedded in Wed pages;

java mainly runs on the server side;

javascript mainly Runs in the client browser;

java language needs to be compiled before running;

javascript language is interpreted line by line during program running;

java uses strong typing Variable checking, that is, all variables must be declared before compilation;

Javascript language adopts weak typing, that is, no declaration is required before use, but the browser interpreter checks the data type at runtime (console.log( typeof a); The typeof in the browser console returns the data type);

Java requires the main method, @ annotation, and web server to start when running;

Javascript language can be used on the page Listening events on;

Java language code is a language that has nothing to do with HTML;

Javascript language code is a text character format that can be directly embedded in HTML documents and can be dynamically Loading;

Java language can access the local hard disk and call the data on the hard disk;

Javascript language cannot access the local hard disk, cannot store data on the server, and is not allowed to modify network documents. Modification and deletion can only be achieved through the browser for information browsing or dynamic interaction;

java language depends on jdk programming;

javascript language depends on the browser and has nothing to do with the operating system;

Java’s basic data types

Recommended tutorial: "java learning"

1) Four integer types (byte, short, int, long):

byte: 8 bits, used to represent the smallest data unit, such as data in a file, -128~127

short: 16 bits, rarely used, -32768~ 32767

int: 32 bits, the most commonly used, -2^31-1~2^31 (2.1 billion)

long: 64 bits, the second most commonly used

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Precautions : int i=5; // 5 is called a direct quantity (or literal), that is, a constant written directly. Integer literals are of type int by default, so add L or l after the defined long data. Variables with less than 32 digits are calculated as int results. The cast operator has higher precedence than the mathematical operator. See Constants and Variables for examples.

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2) Two types of floating point numbers (float, double):

float: 32 bits, suffix F or f, 1 sign bit, 8 bit exponent , 23 valid mantissas.

double: 64 bits, most commonly used, suffix D or d, 1 sign bit, 11 bits exponent, 52 bits effective tail

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Notes: Binary floating point number: 1010100010 =101010001.0*2=10101000.10*2^10 (2nd power)=1010100.010*2^11 (3rd power)= . 1010100010*2^1010 (10th power) Mantissa: . 1010100010 Index: 1010 Base: 2 Floating point number Literal values ​​are of double type by default, so add F or f after the defined float type data; the double type does not need to write a suffix, but you must write D or X. )short. The range of float is larger than that of long and the exponent can be very large. Floating point numbers are inexact, and floating point numbers cannot be compared accurately.

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3) A character type (char):

char: 16 bits, an integer type, 1 character enclosed in single quotes (can be a Chinese character), using Unicode code to represent characters, 0~2^16-1 (65535).

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Notes: Cannot be 0 characters. Escape characters: \n Line feed \r Carriage return \t Tab character \" Double quotation mark \\ represents a \ Two characters of char are connected with " " in the middle. The characters are first converted to int type internally, and then the addition operation is performed. The essence of char is Number! Binary, when displayed, it is displayed as characters after "processing".

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4) A Boolean type (boolean): true and false.

Basic data types of JavaScript

Five basic data types (simple data types)

      Undefined 未定义 "undefined"
var a ;
      Null 空引用数据类型 "null"
var a = null;
      Boolean 布尔类型 true/false
var a = false;
      Number 数字类型
整数
浮点数
      String 字符串类型 "" ''
var a ="true";
var a ='hello';

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