Java String類

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 1 package demo03; 2  3 //String類的構造方法 4 public class StringDemo { 5     public static void main(String[] args) { 6          7         String str1 = "str1";                    //定義方式1 8         String str2 = new String("str1");        //定義方式2 9         10         System.out.println(str1);11         System.out.println(str2);12         13         //false str1==str2 比較的是記憶體位址14         System.out.println(str1==str2);            15         //true String類 重寫equals() 比較的是每個字元16         System.out.println(str1.equals(str2));17         18         byte[] by = {97,98,99,100};19         String str3 = new String(by);            //構造方法 String(byte[] bytes) 傳位元組數組20         System.out.println(str3);                //abcd21 22         String str4 = new String(by,1,3);        //構造方法 String(byte[] bytes int offset, int length)23         System.out.println(str4);                //bcd24         25         char[] charArray = {‘i‘,‘j‘,‘k‘};26         String str5 = new String(charArray);    //構造方法 String(char[] value) 傳字元數組27         System.out.println(str5);                //ijk28         29         String str6 = new String(charArray,1,2);//構造方法 String(char[] value, int offset, int count)30         System.out.println(str6);                //jk31         32         33         34         35     }36 }

 1 package demo03; 2  3 public class StringDemo1 { 4     public static void main(String[] args) { 5         String s1 = "abcdefgabcdefg"; 6          7         int length = s1.length();                    //獲得字串長度 8         System.out.println(length);                  //14 9         10         String s2 = s1.substring(0,3);               //截取字串 兩個參數11         String s3 = s1.substring(7);                 //一個參數12         System.out.println(s2);                      //abc13         System.out.println(s3);                      //abcdefg14         15         boolean b1 = s1.startsWith("abc");           //是否以指定字串開始16         System.out.println(b1);                      //true17         18         boolean b2 = s1.endsWith("efg");             //是否以指定字串結尾19         System.out.println(b2);                      //true20         21         boolean b3 = s1.contains("gab");             //是否包含指定字串22         System.out.println(b3);                      //true23         24         int index1 = s1.indexOf(‘c‘);        　　　　 //返回指定字元第一次出現的索引25         int index2 = s1.indexOf(‘x‘);26         System.out.println(index1);            　　　//227         System.out.println(index2);            　　　//-128         29         byte[] bytes = s1.getBytes();        　　　　//字串轉為位元組數組30         for (int i = 0; i < bytes.length; i++) {31             System.out.println(bytes[i]);32         }33         34         char[] ch = s1.toCharArray();               //字串轉為字元數組35         for (int i = 0; i < ch.length; i++) {36             System.out.println(ch[i]);37         }38         39         String s5 = "Abc";40         String s6 = "abc";41         boolean b5 = s5.equals(s6);                //比較字串42         boolean b6 = s5.equalsIgnoreCase(s6);      //比較字串 忽略大小寫43         System.out.println(b5);                    //false44         System.out.println(b6);                    //true45         46         47         48     }49 }

 demo

 1 package demo03; 2  3 public class StringLianXi { 4     public static void main(String[] args) { 5         getCount("fhdkfADfDf123F"); 6         System.out.println(toConvert("aVdfDfd")); 7         System.out.println(getStringCount("helloabc,abc,abcabcfjdklsfjd", "abc")); 8     } 9     10     //擷取指定字串中 大寫字母, 小寫字母, 數字 的個數11     public static void getCount(String s) {12         int upper = 0;13         int lower = 0;14         int digit = 0;15         16         for (int i = 0; i < s.length(); i++) {17             char c = s.charAt(i);18             19             /*if (c>=65 && c<=90) {20                 upper++;21             } else if (c>=97 && c<=122) {22                 lower++;23             } else if (c>=48 && c<=57) {24                 digit++;25             }*/26             27             if (c>=‘A‘ && c<=‘Z‘) {28                 upper++;29             } else if (c>=‘a‘ && c<=‘z‘) {30                 lower++;31             } else if (c>=‘0‘ && c<=‘9‘) {32                 digit++;33             }34         }35         36         System.out.println(upper);37         System.out.println(lower);38         System.out.println(digit);39     }40     41     //將指定字串第一個字母大寫, 其它字母小寫42     public static String toConvert(String s) {43         String first = s.substring(0,1);44         String after = s.substring(1);45         first = first.toUpperCase();46         after = after.toLowerCase();47         48         return first+after;49     }50     51     //查詢指定字串中出現其它字串的次數52     public static int getStringCount(String s, String key) {53         int count = 0;54         int index = 0;55         56         while ((index = s.indexOf(key)) != -1) {57             count++;58             s = s.substring(index+key.length());59         }60         61         return count;62     }63     64 }

 

Java String類