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入门

1 编译：javac Main.java

运行：java Main

2 定义数组

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int arr[] = {2, 4, 5, 3, 1};
int num[] = new int[100];

3 排序

从小到大：Arrays.sort(arr, 0, 5);

从大到小：

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Integer arr[] = {2, 4, 5, 3, 1};
Arrays.sort(arr, 0, 5, Collections.reverseOrder());

4 输入输出

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Scanner in = new Scanner(System.in);
arr[i] = in.nextInt();
System.out.printf("%d ", arr[i]);

5 类的构造方法

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import java.util.*;
class Student {
    int score;
    String name;
    Student(int score, String name) {
        this.score = score;
        this.name = name;
    }
}
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        Student stu = new Student(92, "zyz");
        System.out.println(stu.score);
        System.out.println(stu.name);
    }
}

jdk 安装

https://www.java.com/zh_CN/
点击 所有 java 下载
点击 从何处获取 Java 7？
点击 java 档案 点击 Java SE 7
选择 jdk-7u80-linux-x64.rpm 进行下载

jdk 版本 7u80 64位 jdk-7u80-linux-x64.rpm
操作系统：阿里云CentOS Linux release 7.3.1611 (Core) 

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➜  ~ chmod 777 jdk-7u80-linux-x64.rpm

安装：  
➜  ~ rpm -ivh jdk-7u80-linux-x64.rpm 

默认安装路径 /usr/java  
/usr/java/jdk1.7.0_80

jdk 配置环境变量 

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echo $SHELL
/bin/zsh

在 ~/.zshrc 添加： 

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export JAVA_HOME=/usr/java/jdk1.7.0_80
export CLASSPATH=.:$JAVA_HOME/jre/lib/rt.jar:$JAVA_HOME/lib/dt.jar:$JAVA_HOME/lib/tools.jar

source ~/.zshrc

验证

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java -version
java version "1.7.0_80"
Java(TM) SE Runtime Environment (build 1.7.0_80-b15)
Java HotSpot(TM) 64-Bit Server VM (build 24.80-b11, mixed mode)

Tomcat

Tomcat 是一个 WEB 容器，JavaEE 程序可以在此运行