java 内部类 嵌套类

*:first-child {
margin-top: 0 !important;
}

.markdown-body>*:last-child {
margin-bottom: 0 !important;
}

.markdown-body a:not([href]) {
color: inherit;
text-decoration: none;
}

.markdown-body .anchor {
float: left;
padding-right: 4px;
margin-left: -20px;
line-height: 1;
}

.markdown-body .anchor:focus {
outline: none;
}

.markdown-body p,
.markdown-body blockquote,
.markdown-body ul,
.markdown-body ol,
.markdown-body dl,
.markdown-body table,
.markdown-body pre {
margin-top: 0;
margin-bottom: 16px;
}

.markdown-body hr {
height: 0.25em;
padding: 0;
margin: 24px 0;
background-color: #e1e4e8;
border: 0;
}

.markdown-body blockquote {
padding: 0 1em;
color: #6a737d;
border-left: 0.25em solid #dfe2e5;
}

.markdown-body blockquote>:first-child {
margin-top: 0;
}

.markdown-body blockquote>:last-child {
margin-bottom: 0;
}

.markdown-body kbd {
display: inline-block;
padding: 3px 5px;
font-size: 11px;
line-height: 10px;
color: #444d56;
vertical-align: middle;
background-color: #fafbfc;
border: solid 1px #c6cbd1;
border-bottom-color: #959da5;
border-radius: 3px;
box-shadow: inset 0 -1px 0 #959da5;
}

.markdown-body h1,
.markdown-body h2,
.markdown-body h3,
.markdown-body h4,
.markdown-body h5,
.markdown-body h6 {
margin-top: 24px;
margin-bottom: 16px;
font-weight: 600;
line-height: 1.25;
}

.markdown-body h1 .octicon-link,
.markdown-body h2 .octicon-link,
.markdown-body h3 .octicon-link,
.markdown-body h4 .octicon-link,
.markdown-body h5 .octicon-link,
.markdown-body h6 .octicon-link {
color: #1b1f23;
vertical-align: middle;
visibility: hidden;
}

.markdown-body h1:hover .anchor,
.markdown-body h2:hover .anchor,
.markdown-body h3:hover .anchor,
.markdown-body h4:hover .anchor,
.markdown-body h5:hover .anchor,
.markdown-body h6:hover .anchor {
text-decoration: none;
}

.markdown-body h1:hover .anchor .octicon-link,
.markdown-body h2:hover .anchor .octicon-link,
.markdown-body h3:hover .anchor .octicon-link,
.markdown-body h4:hover .anchor .octicon-link,
.markdown-body h5:hover .anchor .octicon-link,
.markdown-body h6:hover .anchor .octicon-link {
visibility: visible;
}

.markdown-body h1 {
padding-bottom: 0.3em;
font-size: 2em;
border-bottom: 1px solid #eaecef;
}

.markdown-body h2 {
padding-bottom: 0.3em;
font-size: 1.5em;
border-bottom: 1px solid #eaecef;
}

.markdown-body h3 {
font-size: 1.25em;
}

.markdown-body h4 {
font-size: 1em;
}

.markdown-body h5 {
font-size: 0.875em;
}

.markdown-body h6 {
font-size: 0.85em;
color: #6a737d;
}

.markdown-body ul,
.markdown-body ol {
padding-left: 2em;
}

.markdown-body ul ul,
.markdown-body ul ol,
.markdown-body ol ol,
.markdown-body ol ul {
margin-top: 0;
margin-bottom: 0;
}

.markdown-body li>p {
margin-top: 16px;
}

.markdown-body li+li {
margin-top: 0.25em;
}

.markdown-body dl {
padding: 0;
}

.markdown-body dl dt {
padding: 0;
margin-top: 16px;
font-size: 1em;
font-style: italic;
font-weight: 600;
}

.markdown-body dl dd {
padding: 0 16px;
margin-bottom: 16px;
}

.markdown-body table {
display: block;
width: 100%;
overflow: auto;
}

.markdown-body table th {
font-weight: 600;
}

.markdown-body table th,
.markdown-body table td {
padding: 6px 13px;
border: 1px solid #dfe2e5;
}

.markdown-body table tr {
background-color: #fff;
border-top: 1px solid #c6cbd1;
}

.markdown-body table tr:nth-child(2n) {
background-color: #f6f8fa;
}

.markdown-body img {
max-width: 100%;
box-sizing: content-box;
background-color: #fff;
}

.markdown-body code {
padding: 0;
padding-top: 0.2em;
padding-bottom: 0.2em;
margin: 0;
font-size: 85%;
background-color: rgba(27,31,35,0.05);
border-radius: 3px;
}

.markdown-body code::before,
.markdown-body code::after {
letter-spacing: -0.2em;
content: "\A0";
}

.markdown-body pre {
word-wrap: normal;
}

.markdown-body pre>code {
padding: 0;
margin: 0;
font-size: 100%;
word-break: normal;
white-space: pre;
background: transparent;
border: 0;
}

.markdown-body .highlight {
margin-bottom: 16px;
}

.markdown-body .highlight pre {
margin-bottom: 0;
word-break: normal;
}

.markdown-body .highlight pre,
.markdown-body pre {
padding: 16px;
overflow: auto;
font-size: 85%;
line-height: 1.45;
background-color: #f6f8fa;
border-radius: 3px;
}

.markdown-body pre code {
display: inline;
max-width: auto;
padding: 0;
margin: 0;
overflow: visible;
line-height: inherit;
word-wrap: normal;
background-color: transparent;
border: 0;
}

.markdown-body pre code::before,
.markdown-body pre code::after {
content: normal;
}

.markdown-body .full-commit .btn-outline:not(:disabled):hover {
color: #005cc5;
border-color: #005cc5;
}

.markdown-body kbd {
display: inline-block;
padding: 3px 5px;
font: 11px "SFMono-Regular", Consolas, "Liberation Mono", Menlo, Courier, monospace;
line-height: 10px;
color: #444d56;
vertical-align: middle;
background-color: #fafbfc;
border: solid 1px #d1d5da;
border-bottom-color: #c6cbd1;
border-radius: 3px;
box-shadow: inset 0 -1px 0 #c6cbd1;
}

.markdown-body :checked+.radio-label {
position: relative;
z-index: 1;
border-color: #0366d6;
}

.markdown-body .task-list-item {
list-style-type: none;
}

.markdown-body .task-list-item+.task-list-item {
margin-top: 3px;
}

.markdown-body .task-list-item input {
margin: 0 0.2em 0.25em -1.6em;
vertical-align: middle;
}

.markdown-body hr {
border-bottom-color: #eee;
}

/*

github.com style (c) Vasily Polovnyov

*/

.hljs {
display: block;
overflow-x: auto;
padding: 0.5em;
color: #333;
background: #f8f8f8;
}

.hljs-comment,
.hljs-quote {
color: #998;
font-style: italic;
}

.hljs-keyword,
.hljs-selector-tag,
.hljs-subst {
color: #333;
font-weight: bold;
}

.hljs-number,
.hljs-literal,
.hljs-variable,
.hljs-template-variable,
.hljs-tag .hljs-attr {
color: #008080;
}

.hljs-string,
.hljs-doctag {
color: #d14;
}

.hljs-title,
.hljs-section,
.hljs-selector-id {
color: #900;
font-weight: bold;
}

.hljs-subst {
font-weight: normal;
}

.hljs-type,
.hljs-class .hljs-title {
color: #458;
font-weight: bold;
}

.hljs-tag,
.hljs-name,
.hljs-attribute {
color: #000080;
font-weight: normal;
}

.hljs-regexp,
.hljs-link {
color: #009926;
}

.hljs-symbol,
.hljs-bullet {
color: #990073;
}

.hljs-built_in,
.hljs-builtin-name {
color: #0086b3;
}

.hljs-meta {
color: #999;
font-weight: bold;
}

.hljs-deletion {
background: #fdd;
}

.hljs-addition {
background: #dfd;
}

.hljs-emphasis {
font-style: italic;
}

.hljs-strong {
font-weight: bold;
}

/* Flowchart variables */
/* Sequence Diagram variables */
/* Gantt chart variables */
.mermaid .label {
color: #333;
}
.node rect,
.node circle,
.node ellipse,
.node polygon {
fill: #ECECFF;
stroke: #CCCCFF;
stroke-width: 1px;
}
.edgePath .path {
stroke: #333333;
}
.edgeLabel {
background-color: #e8e8e8;
}
.cluster rect {
fill: #ffffde !important;
rx: 4 !important;
stroke: #aaaa33 !important;
stroke-width: 1px !important;
}
.cluster text {
fill: #333;
}
.actor {
stroke: #CCCCFF;
fill: #ECECFF;
}
text.actor {
fill: black;
stroke: none;
}
.actor-line {
stroke: grey;
}
.messageLine0 {
stroke-width: 1.5;
stroke-dasharray: "2 2";
marker-end: "url(#arrowhead)";
stroke: #333;
}
.messageLine1 {
stroke-width: 1.5;
stroke-dasharray: "2 2";
stroke: #333;
}
#arrowhead {
fill: #333;
}
#crosshead path {
fill: #333 !important;
stroke: #333 !important;
}
.messageText {
fill: #333;
stroke: none;
}
.labelBox {
stroke: #CCCCFF;
fill: #ECECFF;
}
.labelText {
fill: black;
stroke: none;
}
.loopText {
fill: black;
stroke: none;
}
.loopLine {
stroke-width: 2;
stroke-dasharray: "2 2";
marker-end: "url(#arrowhead)";
stroke: #CCCCFF;
}
.note {
stroke: #aaaa33;
fill: #fff5ad;
}
.noteText {
fill: black;
stroke: none;
font-family: 'trebuchet ms', verdana, arial;
font-size: 14px;
}
/** Section styling */
.section {
stroke: none;
opacity: 0.2;
}
.section0 {
fill: rgba(102, 102, 255, 0.49);
}
.section2 {
fill: #fff400;
}
.section1,
.section3 {
fill: white;
opacity: 0.2;
}
.sectionTitle0 {
fill: #333;
}
.sectionTitle1 {
fill: #333;
}
.sectionTitle2 {
fill: #333;
}
.sectionTitle3 {
fill: #333;
}
.sectionTitle {
text-anchor: start;
font-size: 11px;
text-height: 14px;
}
/* Grid and axis */
.grid .tick {
stroke: lightgrey;
opacity: 0.3;
shape-rendering: crispEdges;
}
.grid path {
stroke-width: 0;
}
/* Today line */
.today {
fill: none;
stroke: red;
stroke-width: 2px;
}
/* Task styling */
/* Default task */
.task {
stroke-width: 2;
}
.taskText {
text-anchor: middle;
font-size: 11px;
}
.taskTextOutsideRight {
fill: black;
text-anchor: start;
font-size: 11px;
}
.taskTextOutsideLeft {
fill: black;
text-anchor: end;
font-size: 11px;
}
/* Specific task settings for the sections*/
.taskText0,
.taskText1,
.taskText2,
.taskText3 {
fill: white;
}
.task0,
.task1,
.task2,
.task3 {
fill: #8a90dd;
stroke: #534fbc;
}
.taskTextOutside0,
.taskTextOutside2 {
fill: black;
}
.taskTextOutside1,
.taskTextOutside3 {
fill: black;
}
/* Active task */
.active0,
.active1,
.active2,
.active3 {
fill: #bfc7ff;
stroke: #534fbc;
}
.activeText0,
.activeText1,
.activeText2,
.activeText3 {
fill: black !important;
}
/* Completed task */
.done0,
.done1,
.done2,
.done3 {
stroke: grey;
fill: lightgrey;
stroke-width: 2;
}
.doneText0,
.doneText1,
.doneText2,
.doneText3 {
fill: black !important;
}
/* Tasks on the critical line */
.crit0,
.crit1,
.crit2,
.crit3 {
stroke: #ff8888;
fill: red;
stroke-width: 2;
}
.activeCrit0,
.activeCrit1,
.activeCrit2,
.activeCrit3 {
stroke: #ff8888;
fill: #bfc7ff;
stroke-width: 2;
}
.doneCrit0,
.doneCrit1,
.doneCrit2,
.doneCrit3 {
stroke: #ff8888;
fill: lightgrey;
stroke-width: 2;
cursor: pointer;
shape-rendering: crispEdges;
}
.doneCritText0,
.doneCritText1,
.doneCritText2,
.doneCritText3 {
fill: black !important;
}
.activeCritText0,
.activeCritText1,
.activeCritText2,
.activeCritText3 {
fill: black !important;
}
.titleText {
text-anchor: middle;
font-size: 18px;
fill: black;
}
/*

*/
.node text {
font-family: 'trebuchet ms', verdana, arial;
font-size: 14px;
}
div.mermaidTooltip {
position: absolute;
text-align: center;
max-width: 200px;
padding: 2px;
font-family: 'trebuchet ms', verdana, arial;
font-size: 12px;
background: #ffffde;
border: 1px solid #aaaa33;
border-radius: 2px;
pointer-events: none;
z-index: 100;
}

@font-face{font-family:KaTeX_AMS;src:url(fonts/KaTeX_AMS-Regular.eot);src:url(fonts/KaTeX_AMS-Regular.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_AMS-Regular.woff2) format('woff2'),url(fonts/KaTeX_AMS-Regular.woff) format('woff'),url(fonts/KaTeX_AMS-Regular.ttf) format('truetype');font-weight:400;font-style:normal}@font-face{font-family:KaTeX_Caligraphic;src:url(fonts/KaTeX_Caligraphic-Bold.eot);src:url(fonts/KaTeX_Caligraphic-Bold.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Caligraphic-Bold.woff2) format('woff2'),url(fonts/KaTeX_Caligraphic-Bold.woff) format('woff'),url(fonts/KaTeX_Caligraphic-Bold.ttf) format('truetype');font-weight:700;font-style:normal}@font-face{font-family:KaTeX_Caligraphic;src:url(fonts/KaTeX_Caligraphic-Regular.eot);src:url(fonts/KaTeX_Caligraphic-Regular.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Caligraphic-Regular.woff2) format('woff2'),url(fonts/KaTeX_Caligraphic-Regular.woff) format('woff'),url(fonts/KaTeX_Caligraphic-Regular.ttf) format('truetype');font-weight:400;font-style:normal}@font-face{font-family:KaTeX_Fraktur;src:url(fonts/KaTeX_Fraktur-Bold.eot);src:url(fonts/KaTeX_Fraktur-Bold.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Fraktur-Bold.woff2) format('woff2'),url(fonts/KaTeX_Fraktur-Bold.woff) format('woff'),url(fonts/KaTeX_Fraktur-Bold.ttf) format('truetype');font-weight:700;font-style:normal}@font-face{font-family:KaTeX_Fraktur;src:url(fonts/KaTeX_Fraktur-Regular.eot);src:url(fonts/KaTeX_Fraktur-Regular.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Fraktur-Regular.woff2) format('woff2'),url(fonts/KaTeX_Fraktur-Regular.woff) format('woff'),url(fonts/KaTeX_Fraktur-Regular.ttf) format('truetype');font-weight:400;font-style:normal}@font-face{font-family:KaTeX_Main;src:url(fonts/KaTeX_Main-Bold.eot);src:url(fonts/KaTeX_Main-Bold.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Main-Bold.woff2) format('woff2'),url(fonts/KaTeX_Main-Bold.woff) format('woff'),url(fonts/KaTeX_Main-Bold.ttf) format('truetype');font-weight:700;font-style:normal}@font-face{font-family:KaTeX_Main;src:url(fonts/KaTeX_Main-Italic.eot);src:url(fonts/KaTeX_Main-Italic.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Main-Italic.woff2) format('woff2'),url(fonts/KaTeX_Main-Italic.woff) format('woff'),url(fonts/KaTeX_Main-Italic.ttf) format('truetype');font-weight:400;font-style:italic}@font-face{font-family:KaTeX_Main;src:url(fonts/KaTeX_Main-Regular.eot);src:url(fonts/KaTeX_Main-Regular.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Main-Regular.woff2) format('woff2'),url(fonts/KaTeX_Main-Regular.woff) format('woff'),url(fonts/KaTeX_Main-Regular.ttf) format('truetype');font-weight:400;font-style:normal}@font-face{font-family:KaTeX_Math;src:url(fonts/KaTeX_Math-Italic.eot);src:url(fonts/KaTeX_Math-Italic.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Math-Italic.woff2) format('woff2'),url(fonts/KaTeX_Math-Italic.woff) format('woff'),url(fonts/KaTeX_Math-Italic.ttf) format('truetype');font-weight:400;font-style:italic}@font-face{font-family:KaTeX_SansSerif;src:url(fonts/KaTeX_SansSerif-Regular.eot);src:url(fonts/KaTeX_SansSerif-Regular.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_SansSerif-Regular.woff2) format('woff2'),url(fonts/KaTeX_SansSerif-Regular.woff) format('woff'),url(fonts/KaTeX_SansSerif-Regular.ttf) format('truetype');font-weight:400;font-style:normal}@font-face{font-family:KaTeX_Script;src:url(fonts/KaTeX_Script-Regular.eot);src:url(fonts/KaTeX_Script-Regular.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Script-Regular.woff2) format('woff2'),url(fonts/KaTeX_Script-Regular.woff) format('woff'),url(fonts/KaTeX_Script-Regular.ttf) format('truetype');font-weight:400;font-style:normal}@font-face{font-family:KaTeX_Size1;src:url(fonts/KaTeX_Size1-Regular.eot);src:url(fonts/KaTeX_Size1-Regular.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Size1-Regular.woff2) format('woff2'),url(fonts/KaTeX_Size1-Regular.woff) format('woff'),url(fonts/KaTeX_Size1-Regular.ttf) format('truetype');font-weight:400;font-style:normal}@font-face{font-family:KaTeX_Size2;src:url(fonts/KaTeX_Size2-Regular.eot);src:url(fonts/KaTeX_Size2-Regular.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Size2-Regular.woff2) format('woff2'),url(fonts/KaTeX_Size2-Regular.woff) format('woff'),url(fonts/KaTeX_Size2-Regular.ttf) format('truetype');font-weight:400;font-style:normal}@font-face{font-family:KaTeX_Size3;src:url(fonts/KaTeX_Size3-Regular.eot);src:url(fonts/KaTeX_Size3-Regular.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Size3-Regular.woff2) format('woff2'),url(fonts/KaTeX_Size3-Regular.woff) format('woff'),url(fonts/KaTeX_Size3-Regular.ttf) format('truetype');font-weight:400;font-style:normal}@font-face{font-family:KaTeX_Size4;src:url(fonts/KaTeX_Size4-Regular.eot);src:url(fonts/KaTeX_Size4-Regular.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Size4-Regular.woff2) format('woff2'),url(fonts/KaTeX_Size4-Regular.woff) format('woff'),url(fonts/KaTeX_Size4-Regular.ttf) format('truetype');font-weight:400;font-style:normal}@font-face{font-family:KaTeX_Typewriter;src:url(fonts/KaTeX_Typewriter-Regular.eot);src:url(fonts/KaTeX_Typewriter-Regular.eot#iefix) format('embedded-opentype'),url(fonts/KaTeX_Typewriter-Regular.woff2) format('woff2'),url(fonts/KaTeX_Typewriter-Regular.woff) format('woff'),url(fonts/KaTeX_Typewriter-Regular.ttf) format('truetype');font-weight:400;font-style:normal}.katex-display{display:block;margin:1em 0;text-align:center}.katex .base,.katex .katex-html,.katex .strut{display:inline-block}.katex-display>.katex{display:inline-block;text-align:initial}.katex{font:400 1.21em KaTeX_Main,Times New 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margin: 64px 0 32px 0;
height: 1px;
}
.footnotes {
font-size: 90%;
padding-left: 16px;
}
li.footnote-item > p {
margin: 8px 0;
}
.success,
.info,
.warning,
.danger {
padding: 15px;
margin-bottom: 20px;
border: 1px solid transparent;
border-radius: 4px;
}
.success > p:last-child,
.info > p:last-child,
.warning > p:last-child,
.danger > p:last-child {
margin-bottom: 0;
}
.success {
color: #3c763d;
background-color: #dff0d8;
border-color: #d6e9c6;
}
.info {
color: #31708f;
background-color: #d9edf7;
border-color: #bce8f1;
}
.warning {
color: #8a6d3b;
background-color: #fcf8e3;
border-color: #faebcc;
}
.danger {
color: #a94442;
background-color: #f2dede;
border-color: #ebccd1;
}
abbr[title] {
cursor: help;
border-bottom: 1px dotted #777;
}
ul.table-of-contents {
list-style-type: none;
}
ul.table-of-contents li {
margin: 4px 0;
}
.markdown-body table {
width: auto;
display: table;
}
.markdown-body table td,
.markdown-body table th {
word-break: break-all;
}
.markdown-body.ace_search .highlight pre,
.markdown-body.ace_search pre {
overflow: visible !important;
width: fit-content !important;
}
-->

java 内部类 嵌套类

概述

java允许我们把一个类a定义在另一个类b里面,那么这个类a就叫做内部类。例如如下面：

1. 如果内部类似Non-static的那么被称作内部类

class OuterClass {
   ...
   class NestedClass {
       ...
   }
}

1. 如果内部类是static 的那么被称作嵌套类或者内部静态类

class OuterClass {
  ...
  static class StaticNestedClass {
      ...
  }

}

使用方法

1. 普通的内部类

Outer o = new Outer();
Outer.Inner i = o.new Inner();

• 内部类的对象只能在与其外部类相关联的情况下才能被创建。
• 内部类访问外部类实例时可以使用Outer.this,创建内部类实例时使用外部类的实例对象 .new Inner()
• 内部类对象隐含地保存了一个指向外部类对象的引用，每一个非静态内部类的实例都链接到一个外部类的实例上

1. 静态嵌套类

  Outer.Inner i = new Outer.Inner();

• 如果不需要内部类与其外部类对象之间有联系,可以将内部类声明为static.
• 不能访问非静态的外围成员

注意

• 如果一个类要被声明为static的，只有一种情况，就是静态内部类。
• 静态内部类跟静态方法一样，只能访问静态的成员变量和方法，不能访问非静态的方法和属性，但是普通内部类可以访问任意外部类的成员变量和方法
• 静态内部类可以声明普通成员变量和方法以及static成员变量和方法，而普通内部类不能声明static成员变量和方法。

为什么需要内部类

内部类的使用场景

1. 先定义一个抽象类

/**
* Selector迭代器
*/
public abstract class Selector<T> {
  public  void ff(){
      System.out.println(this.getClass().getName());
  }
  abstract boolean hasNext();
  abstract T next();
}

再定义一个Sequence类

/**
* 用类包装一个Integer的数组,并实现添加 通过继承Selector迭代遍历
*/
public class Sequence  extends Selector<Integer>{
  private Object  [] items;
  private int next =0;

  public Sequence(int size){
      items=new Object[size];
  }
  public void add(int x){
      if(next <items.length){
          items[next]=x;
          next++;
      }
  }

  /************************************实现抽象类*/

  private  int index=0;
  @Override
  boolean hasNext() {
      return !(index==items.length);
  }

  @Override
  Integer next() {
      Integer value=null;
      if( hasNext()){
          value=Integer.parseInt(items[index].toString()) ;
          index++;
      }
      return value;

  }
}

我们定义一个Sequence类来包装了一个Object的数组,里面封装了添加初始化操作,通过继承了Selector<T> 来实现了迭代遍历功能。 这时如果我们需要Sequence再继承其他类怎么办？比如现在有一个类SequenceBiz

/**
* Sequence需要继承的业务
*/
public class SequenceBiz {
 public void log()
 {
     //dosomestring 一些需要Sequence继承的业务
     System.out.println(this.getClass().getName()+"我记录了日志");
 }
}

这个时候可以使用内部类来解决

1. 使用内部类

/**
* 用类包装一个Object的数组,并使用内部类通过继承Selector迭代遍历
* 继承SequenceBiz 来处理其他业务
*/
public class Sequence1 extends SequenceBiz{
 private Object  [] items;
 private int next =0;

 public Sequence1(int size){
     items=new Object[size];
 }
 public void add(int x){
     if(next <items.length){
         items[next]=x;
         next++;
     }
 }
 private class SequenceSelector extends Selector<Integer>{
     private  int index=0;
     @Override
     public boolean hasNext() {
         return !(index==items.length);
     }

     @Override
     public Integer next() {
         Integer value=null;
         if( hasNext()){
             value=Integer.parseInt(items[index].toString()) ;
             index++;
         }
         return value;

     }
 }
 /**
  * 返回迭代器
  * @return
  */
 public  Selector getSelector()
 {
     return new SequenceSelector();
 }

}

我们来测试一下

public class TestInnerClass {
 public static  void main(String[] args)
 {
//        Sequence sequence=new Sequence(5);
//        for (int i=0;i<5;i++){
//            sequence.add(i);
//        }
//        while (sequence.hasNext()){
//            System.out.println(sequence.next());
//        }
     Sequence1 sequence1=new Sequence1(5);
     for (int i=0;i<5;i++){
         sequence1.add(i);
     }
     Selector selector=sequence1.getSelector();
     while (selector.hasNext()){
         System.out.println(selector.next());
     }
     sequence1.log();
 }
}

我们来看内部类的好处：

1. 使用内部类解决了java中不能继承多个类的问题
2. Sequence1创建的private内部类来实现Selector 隐藏了Selector的具体实现。(jdk源码中ArrayList的迭代器就是这种方法)
3. 嵌套小类会使代码更靠近使用位置,使代码更加利于维护、

静态内部类的场景

1. 普通类中创建一个静态类

   public class Outer {
   private String name;
   private int age;  

   public static class Builder {
       private String name;
       private int age;  

       public Builder(int age) {
           this.age = age;
       }  

       public Builder withName(String name) {
           this.name = name;
           return this;
       }  

       public Builder withAge(int age) {
           this.age = age;
           return this;
       }  

       public Outer build() {
           return new Outer(this);
       }
   }  

   private Outer(Builder b) {
       this.age = b.age;
       this.name = b.name;
   }
}

静态内部类调用外部类的构造函数，来构造外部类，由于静态内部类可以被单独初始化说有在外部就有以下实现。即Builder design pattern（生成器设计模式） 我们可以在main中使用

  调用  Outer outer = new Outer.Builder(2).withName("Yang Liu").build();

1. 总结

• 如果类的构造器或者静态工厂中有多个参数，设计这样类时，最好使用builder模式，特别是大多数参数都是可选的时候。
• 如果现在不能确定参数的个数，使用构造器即builder模式。
• 静态内部类提高了封装性，和代码的可读性。

1. 接口中的内部类 在接口中我们定义的内部类只能是静态内部类。关于使用场景可以参考shiro框架中Subject接口。

/**
*生成器设计模式实现用于以简化的方式创建实例
Builder design pattern implementation for creating {@link Subject} instances in a simplified way without requiring knowledge of Shiro's construction techniques.
*
/
public interface Subject {
     public static class Builder {

     }
}

关于这个设计模式可以参考

• https://www.cnblogs.com/zhuyuliang/p/5212746.html
• Builder Design Pattern

总结

• 使用内部类解决了多继承的问题
• 方便将存在一定逻辑关系的类组织在一起，又可以对外界隐藏。
• 使代码更靠近使用位置,使代码更加利于维护

参考

• https://docs.oracle.com/javase/tutorial/java/javaOO/nested.html
• https://www.cnblogs.com/chenssy/p/3388487.html
• https://www.cnblogs.com/dolphin0520/p/3811445.html
• http://blog.csdn.net/hivon/article/details/606312

博客中的源码地址

github地址:https://github.com/yalunwang/java-clump