0.Java介绍（Java语言特点，什么是JDK、JRE、JVM，Java开发注意事项和细节说明，Java转义字符）

0.1.Java语言特点：跨平台性

#mermaid-svg-0aAvN4gBEXwcn2JS .label{font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family);fill:#333;color:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .label text{fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .node rect,#mermaid-svg-0aAvN4gBEXwcn2JS .node circle,#mermaid-svg-0aAvN4gBEXwcn2JS .node ellipse,#mermaid-svg-0aAvN4gBEXwcn2JS .node polygon,#mermaid-svg-0aAvN4gBEXwcn2JS .node path{fill:#ECECFF;stroke:#9370db;stroke-width:1px}#mermaid-svg-0aAvN4gBEXwcn2JS .node .label{text-align:center;fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .node.clickable{cursor:pointer}#mermaid-svg-0aAvN4gBEXwcn2JS .arrowheadPath{fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .edgePath .path{stroke:#333;stroke-width:1.5px}#mermaid-svg-0aAvN4gBEXwcn2JS .flowchart-link{stroke:#333;fill:none}#mermaid-svg-0aAvN4gBEXwcn2JS .edgeLabel{background-color:#e8e8e8;text-align:center}#mermaid-svg-0aAvN4gBEXwcn2JS .edgeLabel rect{opacity:0.9}#mermaid-svg-0aAvN4gBEXwcn2JS .edgeLabel span{color:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .cluster rect{fill:#ffffde;stroke:#aa3;stroke-width:1px}#mermaid-svg-0aAvN4gBEXwcn2JS .cluster text{fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS div.mermaidTooltip{position:absolute;text-align:center;max-width:200px;padding:2px;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family);font-size:12px;background:#ffffde;border:1px solid #aa3;border-radius:2px;pointer-events:none;z-index:100}#mermaid-svg-0aAvN4gBEXwcn2JS .actor{stroke:#ccf;fill:#ECECFF}#mermaid-svg-0aAvN4gBEXwcn2JS text.actor>tspan{fill:#000;stroke:none}#mermaid-svg-0aAvN4gBEXwcn2JS .actor-line{stroke:grey}#mermaid-svg-0aAvN4gBEXwcn2JS .messageLine0{stroke-width:1.5;stroke-dasharray:none;stroke:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .messageLine1{stroke-width:1.5;stroke-dasharray:2, 2;stroke:#333}#mermaid-svg-0aAvN4gBEXwcn2JS #arrowhead path{fill:#333;stroke:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .sequenceNumber{fill:#fff}#mermaid-svg-0aAvN4gBEXwcn2JS #sequencenumber{fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS #crosshead path{fill:#333;stroke:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .messageText{fill:#333;stroke:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .labelBox{stroke:#ccf;fill:#ECECFF}#mermaid-svg-0aAvN4gBEXwcn2JS .labelText,#mermaid-svg-0aAvN4gBEXwcn2JS .labelText>tspan{fill:#000;stroke:none}#mermaid-svg-0aAvN4gBEXwcn2JS .loopText,#mermaid-svg-0aAvN4gBEXwcn2JS .loopText>tspan{fill:#000;stroke:none}#mermaid-svg-0aAvN4gBEXwcn2JS .loopLine{stroke-width:2px;stroke-dasharray:2, 2;stroke:#ccf;fill:#ccf}#mermaid-svg-0aAvN4gBEXwcn2JS .note{stroke:#aa3;fill:#fff5ad}#mermaid-svg-0aAvN4gBEXwcn2JS .noteText,#mermaid-svg-0aAvN4gBEXwcn2JS .noteText>tspan{fill:#000;stroke:none}#mermaid-svg-0aAvN4gBEXwcn2JS .activation0{fill:#f4f4f4;stroke:#666}#mermaid-svg-0aAvN4gBEXwcn2JS .activation1{fill:#f4f4f4;stroke:#666}#mermaid-svg-0aAvN4gBEXwcn2JS .activation2{fill:#f4f4f4;stroke:#666}#mermaid-svg-0aAvN4gBEXwcn2JS .mermaid-main-font{font-family:"trebuchet ms", verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-0aAvN4gBEXwcn2JS .section{stroke:none;opacity:0.2}#mermaid-svg-0aAvN4gBEXwcn2JS .section0{fill:rgba(102,102,255,0.49)}#mermaid-svg-0aAvN4gBEXwcn2JS .section2{fill:#fff400}#mermaid-svg-0aAvN4gBEXwcn2JS .section1,#mermaid-svg-0aAvN4gBEXwcn2JS .section3{fill:#fff;opacity:0.2}#mermaid-svg-0aAvN4gBEXwcn2JS .sectionTitle0{fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .sectionTitle1{fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .sectionTitle2{fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .sectionTitle3{fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .sectionTitle{text-anchor:start;font-size:11px;text-height:14px;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-0aAvN4gBEXwcn2JS .grid .tick{stroke:#d3d3d3;opacity:0.8;shape-rendering:crispEdges}#mermaid-svg-0aAvN4gBEXwcn2JS .grid .tick text{font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-0aAvN4gBEXwcn2JS .grid path{stroke-width:0}#mermaid-svg-0aAvN4gBEXwcn2JS .today{fill:none;stroke:red;stroke-width:2px}#mermaid-svg-0aAvN4gBEXwcn2JS .task{stroke-width:2}#mermaid-svg-0aAvN4gBEXwcn2JS .taskText{text-anchor:middle;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-0aAvN4gBEXwcn2JS .taskText:not([font-size]){font-size:11px}#mermaid-svg-0aAvN4gBEXwcn2JS .taskTextOutsideRight{fill:#000;text-anchor:start;font-size:11px;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-0aAvN4gBEXwcn2JS .taskTextOutsideLeft{fill:#000;text-anchor:end;font-size:11px}#mermaid-svg-0aAvN4gBEXwcn2JS .task.clickable{cursor:pointer}#mermaid-svg-0aAvN4gBEXwcn2JS .taskText.clickable{cursor:pointer;fill:#003163 !important;font-weight:bold}#mermaid-svg-0aAvN4gBEXwcn2JS .taskTextOutsideLeft.clickable{cursor:pointer;fill:#003163 !important;font-weight:bold}#mermaid-svg-0aAvN4gBEXwcn2JS .taskTextOutsideRight.clickable{cursor:pointer;fill:#003163 !important;font-weight:bold}#mermaid-svg-0aAvN4gBEXwcn2JS .taskText0,#mermaid-svg-0aAvN4gBEXwcn2JS .taskText1,#mermaid-svg-0aAvN4gBEXwcn2JS .taskText2,#mermaid-svg-0aAvN4gBEXwcn2JS .taskText3{fill:#fff}#mermaid-svg-0aAvN4gBEXwcn2JS .task0,#mermaid-svg-0aAvN4gBEXwcn2JS .task1,#mermaid-svg-0aAvN4gBEXwcn2JS .task2,#mermaid-svg-0aAvN4gBEXwcn2JS .task3{fill:#8a90dd;stroke:#534fbc}#mermaid-svg-0aAvN4gBEXwcn2JS .taskTextOutside0,#mermaid-svg-0aAvN4gBEXwcn2JS .taskTextOutside2{fill:#000}#mermaid-svg-0aAvN4gBEXwcn2JS .taskTextOutside1,#mermaid-svg-0aAvN4gBEXwcn2JS .taskTextOutside3{fill:#000}#mermaid-svg-0aAvN4gBEXwcn2JS .active0,#mermaid-svg-0aAvN4gBEXwcn2JS .active1,#mermaid-svg-0aAvN4gBEXwcn2JS .active2,#mermaid-svg-0aAvN4gBEXwcn2JS .active3{fill:#bfc7ff;stroke:#534fbc}#mermaid-svg-0aAvN4gBEXwcn2JS .activeText0,#mermaid-svg-0aAvN4gBEXwcn2JS .activeText1,#mermaid-svg-0aAvN4gBEXwcn2JS .activeText2,#mermaid-svg-0aAvN4gBEXwcn2JS .activeText3{fill:#000 !important}#mermaid-svg-0aAvN4gBEXwcn2JS .done0,#mermaid-svg-0aAvN4gBEXwcn2JS .done1,#mermaid-svg-0aAvN4gBEXwcn2JS .done2,#mermaid-svg-0aAvN4gBEXwcn2JS .done3{stroke:grey;fill:#d3d3d3;stroke-width:2}#mermaid-svg-0aAvN4gBEXwcn2JS .doneText0,#mermaid-svg-0aAvN4gBEXwcn2JS .doneText1,#mermaid-svg-0aAvN4gBEXwcn2JS .doneText2,#mermaid-svg-0aAvN4gBEXwcn2JS .doneText3{fill:#000 !important}#mermaid-svg-0aAvN4gBEXwcn2JS .crit0,#mermaid-svg-0aAvN4gBEXwcn2JS .crit1,#mermaid-svg-0aAvN4gBEXwcn2JS .crit2,#mermaid-svg-0aAvN4gBEXwcn2JS .crit3{stroke:#f88;fill:red;stroke-width:2}#mermaid-svg-0aAvN4gBEXwcn2JS .activeCrit0,#mermaid-svg-0aAvN4gBEXwcn2JS .activeCrit1,#mermaid-svg-0aAvN4gBEXwcn2JS .activeCrit2,#mermaid-svg-0aAvN4gBEXwcn2JS .activeCrit3{stroke:#f88;fill:#bfc7ff;stroke-width:2}#mermaid-svg-0aAvN4gBEXwcn2JS .doneCrit0,#mermaid-svg-0aAvN4gBEXwcn2JS .doneCrit1,#mermaid-svg-0aAvN4gBEXwcn2JS .doneCrit2,#mermaid-svg-0aAvN4gBEXwcn2JS .doneCrit3{stroke:#f88;fill:#d3d3d3;stroke-width:2;cursor:pointer;shape-rendering:crispEdges}#mermaid-svg-0aAvN4gBEXwcn2JS .milestone{transform:rotate(45deg) scale(0.8, 0.8)}#mermaid-svg-0aAvN4gBEXwcn2JS .milestoneText{font-style:italic}#mermaid-svg-0aAvN4gBEXwcn2JS .doneCritText0,#mermaid-svg-0aAvN4gBEXwcn2JS .doneCritText1,#mermaid-svg-0aAvN4gBEXwcn2JS .doneCritText2,#mermaid-svg-0aAvN4gBEXwcn2JS .doneCritText3{fill:#000 !important}#mermaid-svg-0aAvN4gBEXwcn2JS .activeCritText0,#mermaid-svg-0aAvN4gBEXwcn2JS .activeCritText1,#mermaid-svg-0aAvN4gBEXwcn2JS .activeCritText2,#mermaid-svg-0aAvN4gBEXwcn2JS .activeCritText3{fill:#000 !important}#mermaid-svg-0aAvN4gBEXwcn2JS .titleText{text-anchor:middle;font-size:18px;fill:#000;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-0aAvN4gBEXwcn2JS g.classGroup text{fill:#9370db;stroke:none;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family);font-size:10px}#mermaid-svg-0aAvN4gBEXwcn2JS g.classGroup text .title{font-weight:bolder}#mermaid-svg-0aAvN4gBEXwcn2JS g.clickable{cursor:pointer}#mermaid-svg-0aAvN4gBEXwcn2JS g.classGroup rect{fill:#ECECFF;stroke:#9370db}#mermaid-svg-0aAvN4gBEXwcn2JS g.classGroup line{stroke:#9370db;stroke-width:1}#mermaid-svg-0aAvN4gBEXwcn2JS .classLabel .box{stroke:none;stroke-width:0;fill:#ECECFF;opacity:0.5}#mermaid-svg-0aAvN4gBEXwcn2JS .classLabel .label{fill:#9370db;font-size:10px}#mermaid-svg-0aAvN4gBEXwcn2JS .relation{stroke:#9370db;stroke-width:1;fill:none}#mermaid-svg-0aAvN4gBEXwcn2JS .dashed-line{stroke-dasharray:3}#mermaid-svg-0aAvN4gBEXwcn2JS #compositionStart{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-0aAvN4gBEXwcn2JS #compositionEnd{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-0aAvN4gBEXwcn2JS #aggregationStart{fill:#ECECFF;stroke:#9370db;stroke-width:1}#mermaid-svg-0aAvN4gBEXwcn2JS #aggregationEnd{fill:#ECECFF;stroke:#9370db;stroke-width:1}#mermaid-svg-0aAvN4gBEXwcn2JS #dependencyStart{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-0aAvN4gBEXwcn2JS #dependencyEnd{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-0aAvN4gBEXwcn2JS #extensionStart{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-0aAvN4gBEXwcn2JS #extensionEnd{fill:#9370db;stroke:#9370db;stroke-width:1}#mermaid-svg-0aAvN4gBEXwcn2JS .commit-id,#mermaid-svg-0aAvN4gBEXwcn2JS .commit-msg,#mermaid-svg-0aAvN4gBEXwcn2JS .branch-label{fill:lightgrey;color:lightgrey;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-0aAvN4gBEXwcn2JS .pieTitleText{text-anchor:middle;font-size:25px;fill:#000;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-0aAvN4gBEXwcn2JS .slice{font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-0aAvN4gBEXwcn2JS g.stateGroup text{fill:#9370db;stroke:none;font-size:10px;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-0aAvN4gBEXwcn2JS g.stateGroup text{fill:#9370db;fill:#333;stroke:none;font-size:10px}#mermaid-svg-0aAvN4gBEXwcn2JS g.statediagram-cluster .cluster-label text{fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS g.stateGroup .state-title{font-weight:bolder;fill:#000}#mermaid-svg-0aAvN4gBEXwcn2JS g.stateGroup rect{fill:#ECECFF;stroke:#9370db}#mermaid-svg-0aAvN4gBEXwcn2JS g.stateGroup line{stroke:#9370db;stroke-width:1}#mermaid-svg-0aAvN4gBEXwcn2JS .transition{stroke:#9370db;stroke-width:1;fill:none}#mermaid-svg-0aAvN4gBEXwcn2JS .stateGroup .composit{fill:white;border-bottom:1px}#mermaid-svg-0aAvN4gBEXwcn2JS .stateGroup .alt-composit{fill:#e0e0e0;border-bottom:1px}#mermaid-svg-0aAvN4gBEXwcn2JS .state-note{stroke:#aa3;fill:#fff5ad}#mermaid-svg-0aAvN4gBEXwcn2JS .state-note text{fill:black;stroke:none;font-size:10px}#mermaid-svg-0aAvN4gBEXwcn2JS .stateLabel .box{stroke:none;stroke-width:0;fill:#ECECFF;opacity:0.7}#mermaid-svg-0aAvN4gBEXwcn2JS .edgeLabel text{fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .stateLabel text{fill:#000;font-size:10px;font-weight:bold;font-family:'trebuchet ms', verdana, arial;font-family:var(--mermaid-font-family)}#mermaid-svg-0aAvN4gBEXwcn2JS .node circle.state-start{fill:black;stroke:black}#mermaid-svg-0aAvN4gBEXwcn2JS .node circle.state-end{fill:black;stroke:white;stroke-width:1.5}#mermaid-svg-0aAvN4gBEXwcn2JS #statediagram-barbEnd{fill:#9370db}#mermaid-svg-0aAvN4gBEXwcn2JS .statediagram-cluster rect{fill:#ECECFF;stroke:#9370db;stroke-width:1px}#mermaid-svg-0aAvN4gBEXwcn2JS .statediagram-cluster rect.outer{rx:5px;ry:5px}#mermaid-svg-0aAvN4gBEXwcn2JS .statediagram-state .divider{stroke:#9370db}#mermaid-svg-0aAvN4gBEXwcn2JS .statediagram-state .title-state{rx:5px;ry:5px}#mermaid-svg-0aAvN4gBEXwcn2JS .statediagram-cluster.statediagram-cluster .inner{fill:white}#mermaid-svg-0aAvN4gBEXwcn2JS .statediagram-cluster.statediagram-cluster-alt .inner{fill:#e0e0e0}#mermaid-svg-0aAvN4gBEXwcn2JS .statediagram-cluster .inner{rx:0;ry:0}#mermaid-svg-0aAvN4gBEXwcn2JS .statediagram-state rect.basic{rx:5px;ry:5px}#mermaid-svg-0aAvN4gBEXwcn2JS .statediagram-state rect.divider{stroke-dasharray:10,10;fill:#efefef}#mermaid-svg-0aAvN4gBEXwcn2JS .note-edge{stroke-dasharray:5}#mermaid-svg-0aAvN4gBEXwcn2JS .statediagram-note rect{fill:#fff5ad;stroke:#aa3;stroke-width:1px;rx:0;ry:0}:root{--mermaid-font-family: '"trebuchet ms", verdana, arial';--mermaid-font-family: "Comic Sans MS", "Comic Sans", cursive}#mermaid-svg-0aAvN4gBEXwcn2JS .error-icon{fill:#522}#mermaid-svg-0aAvN4gBEXwcn2JS .error-text{fill:#522;stroke:#522}#mermaid-svg-0aAvN4gBEXwcn2JS .edge-thickness-normal{stroke-width:2px}#mermaid-svg-0aAvN4gBEXwcn2JS .edge-thickness-thick{stroke-width:3.5px}#mermaid-svg-0aAvN4gBEXwcn2JS .edge-pattern-solid{stroke-dasharray:0}#mermaid-svg-0aAvN4gBEXwcn2JS .edge-pattern-dashed{stroke-dasharray:3}#mermaid-svg-0aAvN4gBEXwcn2JS .edge-pattern-dotted{stroke-dasharray:2}#mermaid-svg-0aAvN4gBEXwcn2JS .marker{fill:#333}#mermaid-svg-0aAvN4gBEXwcn2JS .marker.cross{stroke:#333}:root { --mermaid-font-family: "trebuchet ms", verdana, arial;}#mermaid-svg-0aAvN4gBEXwcn2JS {color: rgba(0, 0, 0, 0.75);font: ;}

编译-javac

运行

Test.java程序

Test.class-字节码文件

Win版的JVM

linux版的JVM

Mac版的JVM

...版的JVM

因为有了JVM，同一个Java程序在不同的操作系统中都可以执行，这样实现了Java程序的跨平台性,实现了“一次编译，到处运行”

0.2.什么是JDK、JRE

JDK基本介绍

JDK的全称是 (Java Development Kit, Java开发工具包 )
JDK = JRE + Java的开发工具（java，javac, javadoc, javap等）

JDK是提供给Java开发人员使用的，其中包含了Java的开发工具，也包括了JRE。

JRE基本介绍

JRE的全称是 (Java Runtime Environment, Java运行环境)
JRE = JVM + Java SE标准类库

如果想要运行一个开发好的Java程序，即.class文件（字节码文件）计算机只需要安装JRE即可。

0.3.Java开发注意事项和细节说明

一个源文件中最多只能有一个public类，其它类的个数不限。

public class Hello{}
class Dog{}
class Tiger{}

编译后，每一个类，都对应一个.class

也可以将main方法写在非public类中,然后指定运行非public类，这样入口方法就是非public的main方法

0.4.java转义字符

\t：一个制表位，实现对齐功能

system.out.println('你好\t你好\t你好')；
你好你好你好

\n：换行符
\\：一个\
\"：一个"
\’：一个’
\r：一个回车