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Java基础篇(02)：特殊的String类，和相关扩展API
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‎README.md‎

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### JavaSE基础篇
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[Java基础篇(01)：基本数据类型，核心点整理](https://mp.weixin.qq.com/s?__biz=MzU4Njg0MzYwNw==&mid=2247484444&idx=2&sn=c5590ea2d71a0a358d2f9cd96c3c2b19&chksm=fdf450a4ca83d9b2383032c1aa354a59a0ca6d52981f2a58d6d3142bde7ed1605b4fcde3b4d9&token=1530600379&lang=zh_CN#rd)<br/>
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[Java基础篇(02)：特殊的String类，和相关扩展API](https://mp.weixin.qq.com/s?__biz=MzU4Njg0MzYwNw==&mid=2247484444&idx=1&sn=2cd50529d3d6ff97a9efce6158891c7c&chksm=fdf450a4ca83d9b29f3edf3c4999885278f7e9130a71b1d2f7f54057dcb07a3b95964547e862&token=1530600379&lang=zh_CN#rd)<br/>
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### JavaEE基础
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‎java-se-base-parent/model-data-type/src/main/java/com/data/type/block02string/String01.java‎

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package com.data.type.block02string;
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/**
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* 字符串声明
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*/
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public class String01 {
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public static void main(String[] args) {
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String var1 = "cicada" ;
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String var2 = new String("smile") ;
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}
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}

‎java-se-base-parent/model-data-type/src/main/java/com/data/type/block02string/String02.java‎

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package com.data.type.block02string;
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public class String02 {
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public static void main(String[] args) {
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String var1 = "cicada" ;
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String var2 = "cicada" ;
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// true;true
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System.out.println((var1==var2)+";"+var1.equals(var2));
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String var3 = new String("cicada");
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String var4 = new String("cicada");
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// false;true
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System.out.println((var3==var4)+";"+var3.equals(var4));
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// false;true
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System.out.println((var1==var4)+";"+var2.equals(var4));
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String var5 = "ci"+"cada";
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// true;true
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System.out.println((var1==var5)+";"+var5.equals(var4));
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String var6 = new String02().getVar6 () ;
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// true;true
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System.out.println((var1==var6)+";"+var6.equals(var4));
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}
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public String getVar6 (){
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return "cicada" ;
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}
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}

‎java-se-base-parent/model-data-type/src/main/java/com/data/type/block02string/String03.java‎

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package com.data.type.block02string;
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import java.nio.charset.Charset;
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import java.util.Arrays;
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public class String03 {
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public static void main(String[] args) throws Exception {
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String value = "Hello,知了";
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// UTF-8
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byte[] defaultCharset = value.getBytes(Charset.defaultCharset());
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System.out.println(Arrays.toString(defaultCharset));
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System.out.println(new String(defaultCharset,"UTF-8"));
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// GBK
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byte[] gbkCharset = value.getBytes("GBK");
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System.out.println(Arrays.toString(gbkCharset));
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System.out.println(new String(gbkCharset,"GBK"));
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// ISO-8859-1：表示的字符范围很窄,无法表示中文字符，转换之后无法解码
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byte[] isoCharset = value.getBytes("ISO8859-1");
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System.out.println(Arrays.toString(isoCharset));
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System.out.println(new String(isoCharset,"ISO8859-1"));
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// UTF-16
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byte[] utf16Charset = value.getBytes("UTF-16");
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System.out.println(Arrays.toString(utf16Charset));
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System.out.println(new String(utf16Charset,"UTF-16"));
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}
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}

‎java-se-base-parent/model-data-type/src/main/java/com/data/type/block02string/String04.java‎

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package com.data.type.block02string;
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import java.text.SimpleDateFormat;
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import java.util.Date;
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public class String04 {
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public static void main(String[] args) {
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// 指定位置拼接字符串
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String var1 = formatStr("cicada","smile");
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System.out.println("var1="+var1);
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// 格式化日期：2020-03-07
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SimpleDateFormat format = new SimpleDateFormat("yyyy-MM-dd");
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Date date = new Date() ;
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System.out.println(format.format(date));
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// 浮点数：此处会四舍五入
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double num = 3.14159;
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System.out.print(String.format("浮点类型：%.3f %n", num));
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}
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public static String formatStr (String ...var){
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return String.format("key:%s:route:%s",var);
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}
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}

‎java-se-base-parent/model-data-type/src/main/java/com/data/type/block02string/String05.java‎

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package com.data.type.block02string;
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public class String05 {
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String var1 = "hello" ;
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int[] intArr = {1,2,3};
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public static void main(String[] args) {
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String05 objStr = new String05() ;
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objStr.change(objStr.var1,objStr.intArr);
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// hello 4
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System.out.println(objStr.var1);
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System.out.println(objStr.intArr[2]);
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}
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public void change (String var1,int[] intArr){
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var1 = "world" ;
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intArr[2] = 4 ;
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}
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}

‎java-se-base-parent/model-data-type/src/main/java/com/data/type/block02string/String06.java‎

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package com.data.type.block02string;
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import java.util.UUID;
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public class String06 {
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public static void main(String[] args) {
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System.out.println(StringUtil.getUUid());
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}
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}
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class StringUtil {
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private StringUtil(){}
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public static String getUUid (){
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return UUID.randomUUID().toString().replace("-","");
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}
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}

‎java-se-base-parent/model-data-type/src/main/java/com/data/type/block02string/String07.java‎

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package com.data.type.block02string;
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public class String07 {
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public static void main(String[] args) {
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StringBuffer var = new StringBuffer(2) ;
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var.append("what");
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var.append("when");
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System.out.println(var);
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}
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}

‎java-se-base-parent/model-data-type/src/main/java/com/data/type/block02string/String08.java‎

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package com.data.type.block02string;
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public class String08 {
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public static void main(String[] args) {
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StringBuilder var = new StringBuilder() ;
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var.append("how").append("what") ;
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System.out.println(var);
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}
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}

‎java-se-base-parent/model-data-type/src/main/java/com/data/type/block02string/String09.java‎

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package com.data.type.block02string;
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public class String09 {
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public static void main(String[] args) {
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String var1 = new String("A");
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String var2 = new String("B");
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StringBuffer var3 = new StringBuffer("C");
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StringBuffer var4 = new StringBuffer("D");
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join(var1,var2);
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join(var3,var4);
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//A<>B
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System.out.println(var1+"<>"+var2);
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//C<>DD
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System.out.println(var3+"<>"+var4);
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}
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public static void join (String s1,String s2){
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s1 = s2 ;
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s2 = s1+s2 ;
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}
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public static void join (StringBuffer s1,StringBuffer s2){
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s1 = s2 ;
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s2 = s2.append(s1) ;
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}
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}

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