в 17:44, 31 мая 2010

2010-05-31T17:44:27Z

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== Demonstrate exec(). ==



<source lang="java">
class ExecDemo {
public static void main(String args[]) {
Runtime r = Runtime.getRuntime();
Process p = null;
try {
p = r.exec("notepad");
} catch (Exception e) {
System.out.println("Error executing notepad.");
}
}
}</source>



== Demonstrate totalMemory(), freeMemory() and gc(). ==



<source lang="java">
class MemoryDemo {
public static void main(String args[]) {
Runtime r = Runtime.getRuntime();
long mem1, mem2;
Integer someints[] = new Integer[1000];
System.out.println("Total memory is: " + r.totalMemory());
mem1 = r.freeMemory();
System.out.println("Initial free memory: " + mem1);
r.gc();
mem1 = r.freeMemory();
System.out.println("Free memory after garbage collection: " + mem1);
for (int i = 0; i < 1000; i++)
someints[i] = new Integer(i); // allocate integers
mem2 = r.freeMemory();
System.out.println("Free memory after allocation: " + mem2);
System.out.println("Memory used by allocation: " + (mem1 - mem2));
for (int i = 0; i < 1000; i++)
someints[i] = null;
r.gc(); // request garbage collection
mem2 = r.freeMemory();
System.out.println("Free memory after collecting" + " discarded Integers: " + mem2);
}
}</source>



== Determine when the application is about to exit ==



<source lang="java">
public class Main {
public static void main(String[] argv) throws Exception {
Runtime.getRuntime().addShutdownHook(new Thread() {
public void run() {
System.out.println("Do shutdown work ...");
}
});
}
}</source>



== Display the amount of free memory in the Java Virtual Machine. ==



<source lang="java">
import java.text.DecimalFormat;
public class Main {
public static void main(String[] args) {
DecimalFormat df = new DecimalFormat("0.00");
long freeMem = Runtime.getRuntime().freeMemory();
System.out.println(df.format(freeMem / 1000000F) + " MB");
}
}</source>



== Display the maximum amount of memory ==



<source lang="java">
import java.text.DecimalFormat;
public class Main {
public static void main(String[] args) {
DecimalFormat df = new DecimalFormat("0.00");
long maxMem = Runtime.getRuntime().maxMemory();
System.out.println(df.format(maxMem / 1000000F) + " MB");
}
}</source>



== Display the total amount of memory in the Java virtual machine. ==



<source lang="java">
import java.text.DecimalFormat;
public class Main {
public static void main(String[] args) {
DecimalFormat df = new DecimalFormat("0.00");
long totalMem = Runtime.getRuntime().totalMemory();
System.out.println(df.format(totalMem / 1000000F) + " MB");
}
}</source>



== Execute a command from code ==



<source lang="java">
public class Main {
public static void main(String[] argv) throws Exception {
// Execute a command without arguments
String command = "ls";
Process child = Runtime.getRuntime().exec(command);
// Execute a command with an argument
command = "ls /tmp";
child = Runtime.getRuntime().exec(command);
}
}</source>



== Execute a command with more than one argument ==



<source lang="java">
public class Main {
public static void main(String[] argv) throws Exception {
// Execute a command with an argument that contains a space
String[] commands = new String[] { "grep", "hello world", "/tmp/f.txt" };
commands = new String[] { "grep", "hello world", "c:\\f.txt" };
Process child = Runtime.getRuntime().exec(commands);
}
}</source>



== Execute system command ==



<source lang="java">
import java.io.IOException;
public class Main {
public static void main(String[] args) throws IOException {
String cmd = "cmd.exe /c start ";
// String file = "c:\\version.txt";
// String file = "http://www.google.ru";
// String file = "c:\\";
// String file = "mailto:author@my.ru";
String file = "mailto:";
Runtime.getRuntime().exec(cmd + file);
}
}</source>



== From Runtime.exec() to ProcessBuilder ==



<source lang="java">
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.Arrays;
public class Main {
public static void main(String args[]) throws IOException {
Runtime runtime = Runtime.getRuntime();
Process process = runtime.exec(args);
InputStream is = process.getInputStream();
InputStreamReader isr = new InputStreamReader(is);
BufferedReader br = new BufferedReader(isr);
String line;
System.out.printf("Output of running %s is:", Arrays.toString(args));
while ((line = br.readLine()) != null) {
System.out.println(line);
}
}
}</source>



== Get Number of Available Processors ==



<source lang="java">
public class Main {
public static void main(String[] args) {
Runtime runtime = Runtime.getRuntime();
int nrOfProcessors = runtime.availableProcessors();
System.out.println("Number of processors available to the Java Virtual Machine: "
+ nrOfProcessors);
}
}
// Number of processors available to the Java Virtual Machine: 2</source>



== Launch a Unix script with Java ==



<source lang="java">
public class Main {
public static void main(String[] argv) throws Exception {
String[] cmd = { "/bin/sh", "-c", "ls > hello" };
Runtime.getRuntime().exec(cmd);
}
}</source>



== Milliseconds elapsed since January 1, 1970 ==



<source lang="java">
import java.util.Properties;
public class SystemApp {
public static void main(String args[]) {
long time = System.currentTimeMillis();
System.out.println(time);
Properties p = System.getProperties();
p.list(System.out);
System.exit(13);
}
}</source>



== Read output from a Command execution ==



<source lang="java">
import java.io.InputStream;
public class Main {
public static void main(String[] argv) throws Exception {
String command = "ls";
Process child = Runtime.getRuntime().exec(command);
InputStream in = child.getInputStream();
int c;
while ((c = in.read()) != -1) {
System.out.println((char) c);
}
in.close();
}
}</source>



== Registering Shutdown Hooks for Virtual Machine ==



<source lang="java">
public class Main implements Runnable {
public void run() {
System.out.println("Shutting down");
}
public static void main(String[] arg) {
Runtime runTime = Runtime.getRuntime();
Main hook = new Main();
runTime.addShutdownHook(new Thread(hook));
}
}</source>



== Send an Input to a Command ==



<source lang="java">
import java.io.OutputStream;
public class Main {
public static void main(String[] argv) throws Exception {
String command = "cat";
Process child = Runtime.getRuntime().exec(command);
OutputStream out = child.getOutputStream();
out.write("some text".getBytes());
out.close();
}
}</source>



== System.getProperty ==



<source lang="java">
class ShowUserDir {
public static void main(String args[]) {
System.out.println(System.getProperty("user.dir"));
}
}
The following properties are available:
file.separator
java.specification.version
java.vm.version
java.class.path
java.vendor
line.separator
java.class.version
java.vendor.url
os.arch
java.rupiler
java.version
os.name
java.ext.dirs
java.vm.name
os.version
java.home
java.vm.specification.name
path.separator
java.io.tmpdir
java.vm.specification.vendor
user.dir
java.library.path
java.vm.specification.version
user.home
java.specification.name
java.vm.vendor
user.name
java.specification.vendor</source>



== Timing program execution. ==



<source lang="java">
class Elapsed {
public static void main(String args[]) {
long start, end;
System.out.println("Timing a for loop from 0 to 1,000,000");
start = System.currentTimeMillis(); // get starting time
for (int i = 0; i < 1000000; i++)
;
end = System.currentTimeMillis(); // get ending time
System.out.println("Elapsed time: " + (end - start));
}
}</source>



== Using arraycopy(). ==



<source lang="java">
class ACDemo {
static byte a[] = { 65, 66, 67, 68, 69, 70, 71, 72, 73, 74 };
static byte b[] = { 77, 77, 77, 77, 77, 77, 77, 77, 77, 77 };
public static void main(String args[]) {
System.out.println("a = " + new String(a));
System.out.println("b = " + new String(b));
System.arraycopy(a, 0, b, 0, a.length);
System.out.println("a = " + new String(a));
System.out.println("b = " + new String(b));
System.arraycopy(a, 0, a, 1, a.length - 1);
System.arraycopy(b, 1, b, 0, b.length - 1);
System.out.println("a = " + new String(a));
System.out.println("b = " + new String(b));
}
}</source>



== Wait until notepad is terminated. ==



<source lang="java">
class ExecDemoFini {
public static void main(String args[]) {
Runtime r = Runtime.getRuntime();
Process p = null;
try {
p = r.exec("notepad");
p.waitFor();
} catch (Exception e) {
System.out.println("Error executing notepad.");
}
System.out.println("Notepad returned " + p.exitValue());
}
}</source>

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в 17:44, 31 мая 2010

Admin: 1 версия