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缘由：

在学习Java的过程中不断用文章进行整理总结（常用功能的Java实现），争取早日能较为熟练的使用Java进行开发。

这一篇主要是对Java杂项知识的一个整理和总结。

正文：

参考解答：

1. 三元操作符；

package com.ixyzero.learn.misc;

/**
 * (条件表达式) ? 表达式1 : 表达式2;
 * 当 (条件表达式) 为 True 时, 执行 表达式1 ; 为 False 时,执行 表达式2 。
 */
public class TestTernaryOperator {
    public static void main(String[] args) {
        int a = 1;
        int b = 5;
        System.out.println("a = " + a + "\nb = " + b);
        int c;
        c = ("" == null || true != false) ? a : b;
        System.out.println("\nc = " + c);

        System.out.println();
        System.out.println("'\"\" == null' is " + ("" == null));
        System.out.println("'true != false' is " + (true != false));
    }
}

2. static 语句块的初始化顺序；

package com.ixyzero.learn.misc;

/**
 * Java里面一个class它的初始化顺序是？
    先 static 再 init 呢？还是直接 init 呢？
    结论：
    先 static 再 main/init 。
 *
print in class static code block
print in main method
print in class init method
hello
 *
 */
public class TestStatic {

    static {
        System.out.println("print in class static code block");
    }

    private TestStatic() {
        System.out.println("print in class init method");
    }
    private void hello() {
        System.out.println("hello");
    }

    public static void main(String[] args) {
        System.out.println("print in main method");

        TestStatic testStatic = new TestStatic();
        testStatic.hello();
    }
}

3. 快速打印当前日期时间的方式；

package com.ixyzero.learn.misc;

import java.text.SimpleDateFormat;

public class TestSubstring {
    public static void main(String[] args) {
        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
        String currentDateTime = df.format(System.currentTimeMillis());

        System.out.println(df.toString()); // java.text.SimpleDateFormat@4f76f1a0
        System.out.println(currentDateTime); // 2018-06-16 16:56:32
    }
}

4. 类型转换的一些情形总结；

package com.ixyzero.learn.misc;

public class TestConvert {
    private static Object returnType() {
        return true;
        // return "haha"; // java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Boolean
    }

    private static Object returnType2() {
        // return true; // java.lang.ClassCastException: java.lang.Boolean cannot be cast to java.lang.String
        return "";
    }

    public static void main(String[] args) {
        boolean tag = (Boolean) returnType();
        if (tag) {
            System.out.println("tag is '" + tag + "'");
        } else {
            System.out.println("tag is '" + tag + "'");
        }

        String tagStr = (String) returnType2();
        if (tagStr  != null && !tagStr.isEmpty()) {
            System.out.println("tagStr is '" + tagStr + "'");
        } else {
            System.out.println("tagStr is '" + tagStr + "'");
        }
    }
}

5. 获取主机名的方法；

package com.ixyzero.learn.misc;

import java.io.IOException;
import java.net.InetAddress;
import java.net.UnknownHostException;
import java.util.Scanner;

public class TestgetHostName {
    public static void main(String[] args) {
        String hostname = null;
        try {
            hostname = InetAddress.getLocalHost().getHostName();
        } catch (UnknownHostException e) {
            e.printStackTrace();
        }
        System.out.println("InetAddress.getLocalHost().getHostName() = " + hostname);

        String os = System.getProperty("os.name").toLowerCase();
        System.out.println("String os = System.getProperty(\"os.name\").toLowerCase() = " + os);
        if (os.contains("win")) {
            try {
                System.out.println("Windows computer name through env:\"" + System.getenv("COMPUTERNAME") + "\"");
                System.out.println("Windows computer name through exec:\"" + execReadToString("hostname") + "\"");
            } catch (IOException e) {
                e.printStackTrace();
            }
        } else if (os.contains("nix") || os.contains("nux") || os.contains("mac os x")) {
            try {
                System.out.println("Unix-like computer name through env:\"" + System.getenv("HOSTNAME") + "\"");
                System.out.println("Unix-like computer name through exec:\"" + execReadToString("hostname") + "\"");
                System.out.println("Unix-like computer name through /etc/hostname:\"" + execReadToString("cat /etc/hostname") + "\"");
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static String execReadToString(String execCommand) throws IOException {
        try (Scanner s = new Scanner(Runtime.getRuntime().exec(execCommand).getInputStream()).useDelimiter("\\A")) {
            return s.hasNext() ? s.next() : "";
        }
    }

}

 

参考链接：

• 【Java】(三)运算符小结(比较、逻辑、三元运算符)
• java 静态代码块执行顺序
• java中静态代码块的用法 static用法详解
• Recommended way to get hostname in Java

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