study of Java

综述

* Java 9 有坑 (+) 11-18
* Java 学习
* Java 学习

备注 每日一更 +代表更新完成。-为待续

java 9 对环境变量做了改动，原来的：.;%JAVA_HOME%\lib\dt.jar;%JAVA_HOME%\lib\tools.jar; 中的dt.jar 和tools.jar 被取消了。所以现在只需要一个__[ . ]__ 嗯。就是这样。

• JAVA_HOME JDK installation path, example: C:\Program Files\Java\jdk-9

• CLASSPATH . (just a dot)

• PATH It may already exists on your system under the name Path, so edit its value by adding at the end: %JAVA_HOME%\bin; If it not exists already, create a new one with the value %JAVA_HOME%\bin;

初始化

• java 保证了保证所有的成员变量都会被初始化

相应的，如基本类型的 int， double 都有相应的固定的初始化值

如自己创建的变量（类） 则会按照类的构造函数进行初始化。

具体可以参加如下代码： 研究 如果仅仅在main 中 new Cupboard(); 时， 产生的结果，不难得到： 初始化的顺序为 static > 成员变量 > 构造函数。

import javax.management.MBeanNotificationInfo;

class Bowl {
    Bowl(int marker) {
        System.out.println("Bowl(" + marker + ")");
    }

    void f1(int marker) {
        System.out.println("f1(" + marker + ")");
    }
}

class Table {
    static Bowl bowl1 = new Bowl(1);

    Table() {
        System.out.println("Table()");
        bowl2.f1(1);
    }

    void f2(int marker) {
        System.out.println("f2(" + marker + ")");
    }

    static Bowl bowl2 = new Bowl(2);
}

class Cupboard {
    Bowl bowl3 = new Bowl(3);
    static Bowl bowl4 = new Bowl(4);

    Cupboard() {
        System.out.println("Cupboard()");
        bowl4.f1(2);
    }

    void f3(int marker) {
        System.out.println("f3(" + marker + ")");
    }

    static Bowl bowl5 = new Bowl(5);
}

public class Main {

    public static void main(String[] args) {
        System.out.println("Creating new Cupboard in main");
        new Cupboard();
        System.out.println("Creating new Cupboard in main");
        new Cupboard();
        table.f2(1);
        cupboard.f3(1);
    }

    static Table table = new Table();
    static Cupboard cupboard = new Cupboard();
}

out put

Bowl(1)
Bowl(2)
Table()
f1(1)
// 特别的应该注意-----------
Bowl(4)
Bowl(5)
Bowl(3)
Cupboard()
f1(2)
// -----------------------
Creating new Cupboard in main
Bowl(3)
Cupboard()
f1(2)
Creating new Cupboard in main
Bowl(3)
Cupboard()
f1(2)
f2(1)
f3(1)