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一、创建第一个工程打开Eclipse,创建HelloWorld程序打开Eclipse选择菜单 File --> New --> Java Project新建工程填写工程名称为HelloWorld右键工程名创建类输入代码public class HelloWorld { public static void main(String[] args) { System.out.println("Hello World"); // TODO Auto-generated constructor stub }}右键运行运行结果显示二、Java基本数据类型char size = 16char min = 0char max = 65535char default = 0byte size = 8byte min = -128byte max = 127byte default = 0short size = 16short min = -32768short max = 32767short default = 0int size = 32int min = -2147483648int max = 2147483647int default = 0long size = 64long min = -9223372036854775808long max = 9223372036854775807long default = 0float size = 32float min = 1.4E-45float max = 3.4028235E38float default = 0.0double size = 64double min = 4.9E-324double max = 1.7976931348623157E308double default = 0.0max int = 2147483647max int to short = -1max int to long = 2147483647max int to float = 2.14748365E9max int to double + 2.147483647E9max int = 2147483647max int + 1 = -2147483648min int = -2147483648min int - 1 = 2147483647max double = 1.7976931348623157E308max double + max double = Infinity- max double = -1.7976931348623157E308- max double - max double = -Infinityboolean value = trueint i/j = 1double i/j = 1.0double (double)i/j = 1.2double i*1.0/j = 1.2三、Java的基本流程控制语句1、If-elseif-else语句主要是根据if的判断结果,选择不同的分支路径,可以if-else嵌套,也可以单独使用if语句,还可以使用 if-else if-else if-…-else进行嵌套public static void testIfElse(int num) { System.out.println("num = " + num); if(num < 10) { System.out.println("num < 10"); } if(num < 100) { System.out.println("num < 100"); }else { System.out.println("num >= 100"); } if(num < 50) { System.out.println("num < 50"); }else if(num>=50 && num <100) { System.out.println("num>=50 && num<100"); }else { System.out.println("num > 100"); } }2、Switch当需要判断的条件比较多时会出现很多的if-else,这种代码的可读性比较差,所以我们可以选择使用switch语句public static void testSwitch(Color color) { switch (color) { case RED: System.out.println("color is " + Color.RED); break; case GREEN: System.out.println("color is " + Color.GREEN); break; case BLACK: System.out.println("color is " + Color.BLACK); break; case YELLOW: System.out.println("color is " + Color.YELLOW); break; default: break; } }3、Forfor循环是依靠三个字段达到循环的目的,三个字段分别是初始值,结束条件,游标移动。也就是设置一个初始条件,每次循环进行一次游标移动,当达到结束条件时推出循环。public static void testFor() { int[] array = new int[10]; for(int i=0;i<10;i++) { array[i] = i; } for(int j:array) { System.out.print(j+" "); } }4、Whilewhile语句是循环语句的另一种方式,当while后面的条件成立时继续循环,当条件不成立是时退出循环,也可以使用do-while嵌套,在do后面首先执行一次循环再到while中进行循环是否继续的检测。public static void testWhile() { int[] array = new int[10]; int i = 0; while(i
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