Java Runtime Class in the java.lang Package

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Java

The Runtime class is used to objectify the execution environment. A Runtime object makes it possible to interact with the current operating system. It provides an interface to the system where the JVM is running, executes operating-system-based programs that are not Java classes, and provides information about the operating system.

Main Runtime Methods

Method	Description
`Process exec(String command)`	Executes the command and returns a reference to the executed process.
`static Runtime getRuntime()`	Returns a reference to the Runtime object.
`void exit(int status)`	Terminates the JVM while returning the status value.
`long freeMemory()`	Returns the amount of memory available to the JVM in bytes.
`long totalMemory()`	Returns the total memory used by the JVM.
`long maxMemory()`	Returns the maximum amount of memory the JVM can use.

Runtime Examples

Example 1)

package com.devkuma.tutorial.java.lang;

public class RuntimeClass {

    public static void main(String[] args) {
        Runtime runtime = Runtime.getRuntime();

        long totalMemory = runtime.totalMemory();
        long freeMemory = runtime.freeMemory();
        long usedMemory = totalMemory - freeMemory;

        System.out.println("Total Memory : " + totalMemory);
        System.out.println("Free Memory : " + freeMemory);
        System.out.println("Used Memory : " + usedMemory);
    }
}

The execution result is as follows.

Total Memory : 128974848
Free Memory : 126929960
Used Memory : 2044888

Example 2) In the example below, write only the code for the relevant OS. If all of them are executed, an error occurs.

package com.devkuma.tutorial.javalang;

import java.io.IOException;

public class RuntimeClass1 {

    public static void main(String[] args) {
        Runtime runtime = Runtime.getRuntime();

        // Execute the command below for Mac.
        try {
            runtime.exec("open /Applications/Contacts.app");
        } catch (IOException e) {
            System.err.println("Error executing Contacts.");
        }

        // Execute the command below for linux.
        try {
            runtime.exec("gedit");
        } catch (IOException e) {
            System.err.println("Error executing gedit.");
        }

        // Execute the command below for windows.
        try {
            runtime.exec("calc.exe");
        } catch (IOException e) {
            System.err.println("Error executing calc.");
        }
    }
}

When executed, the application program appropriate for each OS will run. The execution result is omitted.

References

http://itmore.tistory.com/entry/Runtime-%ED%81%B4%EB%9E%98%EC%8A%A4