SystemクラスのgetProperties()とgetProperty(String)

1.   getProperties()メソッド
getPropertiesで ()メソッドは、Java実行環境、Java仮想マシン、およびシステムに関するいくつかの情報を取得できます.

import java.util.Properties;

public class SystemDemo {
	public static void main(String[] args) {
		Properties properties=System.getProperties();
		//  Java          //1.8.0_121
		System.out.println(properties.getProperty("java.version"));
		//  Java          //Oracle Corporation
		System.out.println(properties.getProperty("java.vendor")); 
		//Java      URL  //http://java.oracle.com/
		System.out.println(properties.getProperty("java.vendor.url"));
		//Java       //C:\Program Files\Java\jre1.8.0_121
		System.out.println(properties.getProperty("java.home"));
		//Java            //1.8
		System.out.println(properties.getProperty("java.specification.version"));
		//Java              //Oracle Corporation
		System.out.println(properties.getProperty("java.specification.vendor"));
		//Java            //Java Platform API Specification
		System.out.println(properties.getProperty("java.specification.name"));
		//Java         //52.0
		System.out.println(properties.getProperty("java.class.version"));
		//Java       //E:\workspace\PropertiesDemo\bin
		System.out.println(properties.getProperty("java.class.path"));
		//             //C:\Program Files\Java\jre1.8.0_121\bin;C:\Windows\Sun\Java\bin;……
		System.out.println(properties.getProperty("java.library.path"));
		//           //C:\Users\hasee\AppData\Local\Temp\
		System.out.println(properties.getProperty("java.io.tmpdir"));
		//     JIT         //null
		System.out.println(properties.getProperty("java.compiler"));
		//              //C:\Program Files\Java\jre1.8.0_121\lib\ext;C:\Windows\Sun\Java\lib\ext
		System.out.println(properties.getProperty("java.ext.dirs"));
		//Java          //25.121-b13
		System.out.println(properties.getProperty("java.vm.version"));
		//Java           //Oracle Corporation
		System.out.println(properties.getProperty("java.vm.vendor"));
		//         //Java HotSpot(TM) 64-Bit Server VM
		System.out.println(properties.getProperty("java.vm.name"));
		//ava           //1.8
		System.out.println(properties.getProperty("java.vm.specification.version"));
		//Java           //Oracle Corporation
		System.out.println(properties.getProperty("java.vm.specification.vendor"));
		//Java          //Java Virtual Machine Specification
		System.out.println(properties.getProperty("java.vm.specification.name"));
		//         //Windows 10
		System.out.println(properties.getProperty("os.name"));
		//         //amd64
		System.out.println(properties.getProperty("os.arch"));
		//          //10.0
		System.out.println(properties.getProperty("os.version"));
		//     （  UNIX     “/”）  //\
		System.out.println(properties.getProperty("file.separator"));
		//     （  UNIX     “:”）  //;
		System.out.println(properties.getProperty("path.separator"));
		//    （  UNIX     “/n”）  //
		System.out.println(properties.getProperty("line.separator"));
		//         //hasee
		System.out.println(properties.getProperty("user.name"));
		//         //C:\Users\hasee
		System.out.println(properties.getProperty("user.home"));
		//            //E:\workspace\PropertiesDemo
		System.out.println(properties.getProperty("user.dir"));
	}
}

getProperty(String)メソッド
SystemのgetProperty(String)メソッドは、System.getProperties().getProperty(String)メソッドに相当します.

import java.util.Properties;

public class SystemDemo {
	public static void main(String[] args) {
		// ：              //E:\workspace\PropertiesDemo
		System.out.println(System.getProperty("user.dir"));
	}
}