字符串

public class DemoClass4String {
   public static void main(String[] args) throws Exception {
      //TODO 字符串有字符组成，字符有三个字节组成，（ascii除外）
      //java.lang.String

      /*
      * 1.字符串 字符 字节
      * */
      char[] ch = {'中', '国'};
      String str = new String(ch);
      System.out.println(str); //中国

      byte[] by = { -28,-72,-83,-27,-101,-67 };
      String str2 = new String(by, "UTF-8");  //中国
      System.out.println(str2);

      /*
      * 2.转移字符
      * */
      String str3 = "\"";
      System.out.println(str3);
      // \' \n(换行符) \t(制表符tab) \\
      System.out.println("\'");  // '
      System.out.println("a\nb"); //a
                                  //b
      System.out.println("a\tb"); //a  b
      System.out.println("a\\b"); //a\b

      /*
      * 3.拼接
      * */
      String str4 = "a" + "b";
      String str5 = "ab";
      System.out.println(str4.hashCode()); //3105
      System.out.println(str5.hashCode());  //3105

      String str6 = "a"+ 1;
      String str7 = 1+ "a";
      System.out.println(str6); //也是字符串：a1
      System.out.println(str7); //也是字符串：1a

      String str8 =1 + 2 + "a";
      System.out.println(str8); //3a 而不是:12a

      //concat() 实现拼接
      String str9 = "a";
      System.out.println(str9.concat("1234")); //a1234

      /*
      *4. 比较，两个字符串里的字符相等就是相等，区分大小写的
      * */
      String str10 = "a";
      String str11 = "b";
      String str12 = "A";
      System.out.println(str10.equals(str11)); //false
      System.out.println(str10.equals(str12)); //false ascii a A 是不同的
      System.out.println(str10.equalsIgnoreCase(str12)); //true 忽略大小写

      /*
      * i = 正数 str10 > str12
      * i = 负数 str10 < str12
      * i =  0   str10 = str12
      * */
      int i = str10.compareTo(str12);
      System.out.println(i); //32 为什么是32？
      System.out.println((byte)'a'); // 97
      System.out.println((byte)'A'); // 65

      //忽略大小写的比较
      int i1 = str10.compareToIgnoreCase(str12);
      System.out.println(i1); // 0

      /*
      * 5. 截断
      * */
      String str13 = "FrankWangSky";
      System.out.println(str13.substring(0, 5)); //Frank  0:开始index(含)，5:结束index(不含)
      System.out.println(str13.substring(0, "Frank".length())); //Frank
      System.out.println(str13.substring(5)); //WangSky

      //split() 分解方法
      String[] wangs = str13.split("Wang");
      for (String wang : wangs) {
         System.out.println(wang);
      }

      //trim() 去掉字符串首尾空格
      String str14 = "  Frank Wang ";
      System.out.println("!"+ str14.trim()+ "!"); //!Frank Wang! 前后空格没有了

      /*
      *6. 替换
      * */
      //replace 纯粹的替换
      String str15 = "FrankWang Frank";
      System.out.println(str15.replace("Frank", "Tom"));

      //replaceAll 根据规则替换，多个不同字符替换为同一个，不同字符用|分割
      String str16 = "FrankWang EmmaJIa";
      System.out.println(str16.replaceAll("Frank|Emma", "Tom"));

      /*
      *7. 转换大小写
      * */
      String str17 = "FrankWang";
      System.out.println(str17.toLowerCase());
      System.out.println(str17.toUpperCase());

      /*
      * 8.查询 toCharArray  getBytes charAt indexOf lastIndexOf
      *        startsWith endsWith isEmpty
      * */
      String str18 = "中国";
      char[] charArray = str18.toCharArray();
      for (char c : charArray) {
         System.out.print(c+" ");
      }
      //上面结果：中 国

      byte[] bytes = str18.getBytes();
      for (byte b : bytes) {
         System.out.print(b+" ");
      }
      //上面结果：-28 -72 -83 -27 -101 -67

      System.out.println();
      //查询指定索引的字符
      System.out.println(str18.charAt(0));

      String str19 = "Frank Wang Frank";
      System.out.println(str19.indexOf("Frank")); //0 字符开始的下标
      System.out.println(str19.lastIndexOf("Frank")); //11 字符开始的下标

      System.out.println(str19.startsWith("F")); //true
      System.out.println(str19.endsWith("Frank")); //true

      String str20 = " ";
      System.out.println(str20.isEmpty()); //false 空字符串，不是空，尽管页面不显示

      /*
      *9. StringBuilder
      * */
      StringBuilder sb = new StringBuilder();
      sb.append("abcdef");
      System.out.println(sb.toString());
      System.out.println(sb.reverse().toString());
      System.out.println(sb.insert(1, "A"));

   }
}