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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) {// outputSystem.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 abcSystem.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); // inputint x; // 声明System.out.println("input int number"); // 提示符x = sc.nextInt(); // 输入的值赋值给xSystem.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