java快速入门1

public class bobo2{

	public static void main(String[] args) {
		System.out.println("bobo is studying java");
	}


}

文件名和公共类名相同且大小写相同，

结束语句带；分号

先是类，类里面是函数

编写.java的源文件，然后用javac编译文件生成.class文件，使用java执行文件java bobo2.java

得到结果

键盘输入小练习：

import java.util.Scanner;

public class Input3{
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		System.out.println("mingzi");
		String name = scanner.next();

		System.out.println("age");
		int age = scanner.nextInt();


		System.out.println("salry");
		double sal = scanner.nextDouble();

		System.out.println("xinxi  ruxia:");
		System.out.println(name + 't'  + age + 'n' + sal);

类型转换

public class ChangeChar{
	public static void main(String[] args) {
		String name = "123456";
		double name2 = Double.parseDouble(name);
		float name3 = Float.parseFloat(name);
		

		System.out.println(name2);
		System.out.println(name3);

}

	}

if  结构记得用{          括起来        }括起来，没有18要乖乖；

import java.util.Scanner;


public class If01{
	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		System.out.println("nide age");
		int age = scanner.nextInt();

		if (age > 18){
			System.out.println("age=" + "t" + age + "chaoguo  18 bie huaihuai");

		}
			
			else{
				System.out.println("meiyou  18 ye yao    guaiguai");
			}
			

	}

}

是不是闰年

import java.util.Scanner;

public class If04{


	public static void main(String[] args) {
		Scanner scanner = new Scanner(System.in);

		System.out.println("qingshuru   year");
		int year =scanner.nextInt();

		if ((year % 4 == 0 && year % 100 != 0) || (year % 400 == 0) ){

			System.out.println(year + "shi  run nian");

		}
			else{
				System.out.println(year + "bubububububushi  run nian");
			}




	}
}