String and Text I/O

Outline The String Class Immutable Strings and Interned Strings String Comparisons String Length, Characters, and Combining Strings Obtaining Substrings Converting, replaceing, and Splitting Strings Finding a Character or a Substring in a String The File Class [Sample code] TestFileClass.java

The String Class A string is a sequence of characters. The String class has 11 constructors and more than 40 methods. Declaration: 1.String S = new String(“Hello Java”); 2.String S = “Hello Java”; 3.Char[] C = { ‘H’, ‘e’, ‘l’, ‘l’, ‘o’, ’ ’, ‘J’, ‘a’, ‘v’, ‘a’ }; String S = new String(C);

Immutable Strings and Interned Strings A string object is immutable; its content cannot be changed. String object for “Java” :StringS String object for “Java” :StringS String object for “html” :String S = “html”;String S = “Java”; X

S1.equals(S2): boolean S1.equalsIgnoreCase(S2): boolean S1.compareTo(S2): int S1.compareToIgnoreCase(S2): int. Java.lang.String 推薦網站 : String Comparisons ( 課本 p.327)

String Length, Characters, and Combining Strings HelloJava S.charAt(0) Java.lang.String S.length(): int S.charAt(index: int): char S.concat(S2): String S.length() = 10 S.charAt(9) A String object is presented using an array internally. ( 課本 p.329)

程式練習 : 1. 宣告一個 String object S1 = “HELLO JAVA ” 2. 宣告一個 String object S2 = “i love Java” 3. 印出 S1 的長度 4. 印出 S1 的第 7 個 char 的內容 5. 用 equals 比較 S1 和 S2, 並印出 true 或 false 6. 用 concat 將 S1 和 S2 字串連接起來, 並印出

Obtaining Substrings Java.lang.String S.substring(beginIndex: int): String S.substring(beginIndex: int, endIndex: int): String HelloJava S.substring(0,5) ( 課本 p.330)

程式練習 : 使用 substring method, 印出 S1 中的第 0~4 個 characters

Converting, replaceing, and Splitting Strings Java.lang.String S.toLowerCase(): String S.toUpperCase(): String S.trim():String S.replace(oldchar, newchar): String S.replaceFirst(oldString, newString): String S.replaceAll(oldString, newString): String S.split (delimiter: String): String[ ] ( 課本 p.331)

程式練習 : 1. 將 S1 轉成 lowercase 印出 2. 將 S2 轉成 uppercase 印出 3. 將 S1 中的 ”JAVA” 子字串 換成 ”C++” 印出 4. 嘗試字串分割 String[] names = S1.split(" "); for(String name:names) { System.out.println(name); }

Finding a Character or a Substring in a String Java.lang.String “JAVA”.indexOf(‘J’) return 0. “JAVA”.indexOf(‘A’) return 1. “JAVA”.indexOf(‘A’,2) return 3. “JAVA”.indexOf(”VA”) return 2. “JAVA”.indexOf(”ABC”,2) return -1. “JAVA”.lastIndexOf(‘A’) return 3.. ( 課本 p.332)

程式練習 : 從 S1 找出子字串 ”JAVA” 印出回傳值

The File Class Create File object. EX: java.io.File file = new java.io.File(“abc.txt”); Writing Data Using PrintWriter. EX: PrintWriter output = new PrintWriter(file); ( 課本 p.349)

程式練習 :  練習 p.349 Listing 9.7 WriteData.java

程式範例 :  TestFileClass.java