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