JAVA SDK 7 http www oracle comtechnetworkjavasedownloadsindex html

開發環境 • JAVA SDK 7 http: //www. oracle. com/technetwork/javase/downloads/index. html • Net. Beans 或 Eclipse Net. Beans https: //netbeans. org/downloads/index. html Eclipse http: //www. eclipse. org/downloads/

第一隻程式 • public class Welcome { • public static void main(String agrs[]) { • System. out. println("Hello JAVA"); • }

print差別 • System. out. print("Hello JAVA"); • System. out. printf("Hello JAVA"); • System. out. println("Hello JAVA");

資料型態 Primitive Types / simple type 範圍 中文 byte (1 byte) -128 ~ 127 位元組 short (2 bytes) -32768 ~ 32767 短整數 int (4 bytes) -2147483648 ~ 2147483647 整數 long (8 bytes) -9223372036854775808 ~ 9223372036854775807 長整數 float (4 bytes) +-3. 4028237*10+38~ +1. 30239846*10 -45 浮點數 double (8 bytes) +1. 76769313486231570*10 +3 08~ 倍準數 4. 94065645841246544*10 324 char (2 bytes) Unicode characters (含中文) 字元 boolean (1 bytes) true或false 布林函數 String 字串 字串

輸入資料 • Scanner input = new Scanner(System. in); • int a = input. next. Int(); • System. out. println(a);

正確應該是 • int a = 10; • int b = 3; • float c = (float)a/b;

猜猜看會顯示什麼 • int a =123; • if(a==1) • System. out. print("1"); • System. out. println("2");

switch • JAVA 7 之後支援String 比較

猜猜看 • int a= 10; • int b = 3; • System. out. println(a/b);

猜猜看 • int a= 10; • double b = 3; • System. out. println(a/b);

作業解說 • • Scanner input = new Scanner(System. in); System. out. println("請輸入直徑"); double r = input. next. Double(); //取得半徑 double ans 1 = 2 * r; //直徑 double ans 2 = 2 * Math. PI * r; //周長 double ans 3 = Math. PI * r; //面積 System. out. printf("直徑=%f 周長=%f 面積=%fn", ans 1, ans 2, ans 3);

作業解說 2 • • • Scanner input = new Scanner(System. in); System. out. println("請輸入五位的數字"); int n = input. next. Int(); if(n>=10000 && n<=99999) { for(int i=4; i>=0; i--) { System. out. printf("%d ", (int)(n/Math. pow(10, i))%10); } } else { System. out. println("你輸入的不是五位數字"); }

作業解說 2偷吃步 • Scanner input = new Scanner(System. in); • System. out. println("請輸入五位的數字"); • String n = input. next. Line(); • if(n. length()==5) { • for(int i=1; i<=5; i++) { • System. out. printf("%s ", n. substring(i-1, i)); • } else { • System. out. println("你輸入的不是五位數字"); • }

Class類別(物件) • public class Cat { • String name = "kitty"; • String sound = "meow"; • int kg = 50; • }

副程式(動作、設定、取得) • public void get. Name() { • } • public String set. Name() { • }

建構子(初始化) • public class Cat { • String name = "kitty"; • String sound = "meow"; • int kg = 50; • • public Cat(String name) { • this. name = name; • }

物件中的物件 • public class Cat { • String name = "kitty"; • String sound = "meow"; • int kg = 50; • Eye lefteye = new Eye(); • Eye righteye = new Eye(); • }

陣列 • int x[]; 或 int []x; 或 int[] x; • x = new int[100]; • String s[]; 或 String[] s; 或 String []s; • s = new String[10];

物件陣列並不會自動初始化 • String s; • System. out. println(s); //NULL • String s[] = new String [2]; • System. out. println(s[0]+s[1]); //ERROR

存取範圍 存取修飾 同一類別 同一套件 子類別 private default OK OK OK protected OK OK OK public OK OK OK 全域 OK

Overloading(多載) • public void set. Name(String name) { • } • public void set. Name(String name 1, String name 2) { • }