java.2.19

在IDEA中，新建项目，步骤如图1.1所示。

新建一个分类包。

在包下面新建一个java类**（类名首字母大写）**

里面书写主函数，简写为psvm，输出helloworld。对于java来说，最小单元是类。调用的输出是为静态static。"+"类似于C中的strcat()。

package test_02; public class Test_02 { public static void main(String[] args) { // output System.out.println("Hello World"); } } D:\java\1.8verson\bin\java.exe ... Hello World 进程已结束，退出代码为 0 package test_02; public class Test_02 { public static void main(String[] args) { // output string // System.out.println("Hello World"); /* output int double float * such as printf in C language */ System.out.printf("%d %.2f", 10, 11.5); } } D:\java\1.8verson\bin\java.exe 10 11.50 进程已结束，退出代码为 0 package test_02; public class Test_02 { public static void main(String[] args) { // output string // System.out.println("Hello World"); /* output int double float * such as printf in C language */ // System.out.printf("%d %.2f", 10, 11.5); // result abc System.out.println("a" + "b" + "c"); } } D:\java\1.8verson\bin\java.exe abc 进程已结束，退出代码为 0

对于数组，分为静态和动态的初始化及输出。

package test_02; public class Test_02 { public static void main(String[] args) { // output string // System.out.println("Hello World"); /* output int double float * such as printf in C language */ // System.out.printf("%d %.2f", 10, 11.5); // result abc // System.out.println("a" + "b" + "c"); // 动态数组 int []a = new int[10]; for (int i = 0; i < a.length; i++) { a[i] = i * 2; // input } for (int i = 0; i < a.length; i++) { System.out.print(a[i] + " "); // output } } } D:\java\1.8verson\bin\java.exe 0 2 4 6 8 10 12 14 16 18 进程已结束，退出代码为 0 package test_02; public class Test_02 { public static void main(String[] args) { // output string // System.out.println("Hello World"); /* output int double float * such as printf in C language */ // System.out.printf("%d %.2f", 10, 11.5); // result abc // System.out.println("a" + "b" + "c"); // 动态数组 int []a = new int[10]; for (int i = 0; i < a.length; i++) { a[i] = i * 2; // input } for (int i = 0; i < a.length; i++) { System.out.print(a[i] + " "); // output } System.out.println(); // output to enter. int []b = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; for (int i = 0; i < b.length; i++) { System.out.print(b[i] + " "); // output } } } D:\java\1.8verson\bin\java.exe 0 2 4 6 8 10 12 14 16 18 1 2 3 4 5 6 7 8 9 10 进程已结束，退出代码为 0

输入

package test_02; import java.util.Scanner; public class Test_02 { public static void main(String[] args) { // output string // System.out.println("Hello World"); /* output int double float * such as printf in C language */ // System.out.printf("%d %.2f", 10, 11.5); // result abc // System.out.println("a" + "b" + "c"); // 动态数组 int []a = new int[10]; for (int i = 0; i < a.length; i++) { a[i] = i * 2; // input } for (int i = 0; i < a.length; i++) { System.out.print(a[i] + " "); // output } System.out.println(); // output to enter. int []b = {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}; for (int i = 0; i < b.length; i++) { System.out.print(b[i] + " "); // output } System.out.println(); // output to enter. /* 对象方法， 开辟空间， 类声明一个对象， 新建一个， 调用 */ Scanner sc = new Scanner(System.in); // input int x; // 声明 System.out.println("input int number"); // 提示符 x = sc.nextInt(); // 输入的值赋值给x System.out.println("x = " + x); // output } } D:\java\1.8verson\bin\java.exe 0 2 4 6 8 10 12 14 16 18 1 2 3 4 5 6 7 8 9 10 input int number 20 x = 20 进程已结束，退出代码为 0