Java by API/java.lang/System

System: arraycopy(Object src, int srcPos, Object dest, int destPos, int length)

    
/*
 * Output:
 
array2: 0 1 2 3 4 0 0 0 0 0

 */
public class MainClass {
  public static void main(String args[]) {
    int array1[] = { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9 };
    int array2[] = { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 };
    System.arraycopy(array1, 0, array2, 0, 5);
    System.out.print("array2: ");
    System.out.print(array2[0] + " ");
    System.out.print(array2[1] + " ");
    System.out.print(array2[2] + " ");
    System.out.print(array2[3] + " ");
    System.out.print(array2[4] + " ");
    System.out.print(array2[5] + " ");
    System.out.print(array2[6] + " ");
    System.out.print(array2[7] + " ");
    System.out.print(array2[8] + " ");
    System.out.println(array2[9]);
  }
}

System: clearProperty(String key)

    
public class Main {
  public static void main(String[] a) {
    String oldValue = System.clearProperty("java.class.path");
    System.setProperty("user.dir", "C:/MyProg");
    System.out.println(System.getProperty("user.dir"));
  }
}

System: console()

    
import java.io.Console;
import java.io.IOException;
import java.util.Arrays;
public class Main {
  public static void main(String args[]) throws IOException {
    Console c = System.console();
    if (c == null) {
      System.err.println("No console.");
      System.exit(1);
    }
    String login = c.readLine("Enter your login: ");
    char[] oldPassword = c.readPassword("Enter your old password: ");
    if (verify(login, oldPassword)) {
      boolean noMatch;
      do {
        char[] newPassword1 = c.readPassword("Enter your new password: ");
        char[] newPassword2 = c.readPassword("Enter new password again: ");
        noMatch = !Arrays.equals(newPassword1, newPassword2);
        if (noMatch) {
          c.format("Passwords don"t match. Try again.%n");
        } else {
          change(login, newPassword1);
          c.format("Password for %s changed.%n", login);
        }
        Arrays.fill(newPassword1, " ");
        Arrays.fill(newPassword2, " ");
      } while (noMatch);
    }
    Arrays.fill(oldPassword, " ");
  }
  // Dummy verify method.
  static boolean verify(String login, char[] password) {
    return true;
  }
  // Dummy change method.
  static void change(String login, char[] password) {
  }
}

System: currentTimeMillis()

    
/*
 * Output:
 
1145995967880
 */
public class MainClass {
  public static void main(String args[]) {
    System.out.println(System.currentTimeMillis());
  }
}

System.exit(int status)

    
public class MainClass {
  public static void main(String[] args) throws Exception {
    Object f = new Object() {
      public void finalize() {
        System.out.println("Running finalize()");
      }
    };
    Runtime.getRuntime().addShutdownHook(new Thread() {
      public void run() {
        System.out.println("Running Shutdown Hook");
      }
    });
    f = null;
    System.gc();
    System.out.println("Calling System.exit()");
    System.exit(0);
  }
}

System: getenv(String key)

    
/*
 System.getenv("PATH") = C:\WINDOWS\system32;C:\WINDOWS;C:\WINDOWS\System32\Wbem;C:\WINDOWS\system32\nls;....
 * */

public class MainClass {
  public static void main(String[] a) throws Exception {
    System.out.println("System.getenv(\"PATH\") = " + System.getenv("PATH"));
  }
}

System: getProperties()

    
/*
 * Output:
-- listing properties --
java.runtime.name=Java(TM) 2 Runtime Environment, Stand...
java.vm.version=1.5.0-b64
java.vm.vendor=Sun Microsystems Inc.
java.vendor.url=http://java.sun.ru/
path.separator=;
java.vm.name=Java HotSpot(TM) Client VM
file.encoding.pkg=sun.io
user.country=US
sun.os.patch.level=Service Pack 2
java.vm.specification.name=Java Virtual Machine Specification
java.runtime.version=1.5.0-b64
java.awt.graphicsenv=sun.awt.Win32GraphicsEnvironment
...
...
 */
import java.util.Properties;
public class MainClass {
  public static void main(String[] args) {
    Properties properties = System.getProperties();
    properties.list(System.out);
  }
}

System: getProperty(String key, String def)

    
public class Main{
  public static void main(String[] args){
     System.out.println(System.getProperty("password","defaultPassword")); 
  }
}

System: getProperty(String name)

    
/*
 * Output: 
C:\Java_Dev\workspace\cal 
 */
public class MainClass {
  public static void main(String args[]) {
    System.out.println(System.getProperty("user.dir"));
  }
}

System.getProperty ("user.dir")

    
public class Main{
  public static void main(String[] args){
    System.out.println(System.getProperty ("user.dir"));      
  }
}

System.identityHashCode(Object x)

  
import java.io.File;
public class Main {
  public static void main(String[] argv) throws Exception {
    File file1 = new File("a");
    File file2 = new File("a");
    File file3 = new File("b");
    int ihc1 = System.identityHashCode(file1);
    System.out.println(ihc1);
    int ihc2 = System.identityHashCode(file2);
    System.out.println(ihc2);
    int ihc3 = System.identityHashCode(file3);
    System.out.println(ihc3);
  }
}

System.in

    
/*
 * Output:
 */
import java.io.BufferedReader;
import java.io.InputStreamReader;
public class MainClass {
  public static void main(String args[]) {
    try {
      InputStreamReader isr = new InputStreamReader(System.in);
      BufferedReader br = new BufferedReader(isr);
      while (true) {
        System.out.print("Radius? ");
        String str = br.readLine();
        double radius;
        try {
          radius = Double.valueOf(str).doubleValue();
        } catch (NumberFormatException nfe) {
          System.out.println("Incorrect format!");
          continue;
        }
        if (radius <= 0) {
          System.out.println("Radius must be positive!");
          continue;
        }
        double area = Math.PI * radius * radius;
        System.out.println("Area is " + area);
        return;
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }
}

System.in.read()

    
import java.io.IOException;
public class MainClass {
  public static void main(String[] args) {
    int inChar;
    System.out.println("Enter a Character:");
    try {
      inChar = System.in.read();
      System.out.print("You entered ");
      System.out.println(inChar);
    }
    catch (IOException e){
      System.out.println("Error reading from user");
    }
  }
}

System: nanoTime()

    
public class Main {
  public static void main(String[] args) {
    long start = System.nanoTime();
    // block of code to time
    long end = System.nanoTime();
    System.out.println("It took " + (end - start) + " nanoseconds");
  }
}

System.out

    
/*
 * Output:
true
A
500
40000
45.67
45.67
Hello
99
 
 */
import java.io.PrintWriter;
public class MainClass {
  public static void main(String args[]) {
    try {
      PrintWriter pw = new PrintWriter(System.out);
      // Experiment with some methods
      pw.println(true);
      pw.println("A");
      pw.println(500);
      pw.println(40000L);
      pw.println(45.67f);
      pw.println(45.67);
      pw.println("Hello");
      pw.println(new Integer("99"));
      // Close print writer
      pw.close();
    } catch (Exception e) {
      System.out.println("Exception: " + e);
    }
  }
}

System.setErr(PrintStream err)

    
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintStream;
import java.sql.Timestamp;
public class MainClass {
  public static void main(String[] args) {
    try {
      String FILE = "c:\\systemin.txt";
      FileOutputStream outStr = new FileOutputStream(FILE, true);
      PrintStream printStream = new PrintStream(outStr);
      System.setErr(printStream);
      Timestamp now = new Timestamp(System.currentTimeMillis());
      System.out.println(now.toString() + ": This is text that should go to the file");
      outStr.close();
      printStream.close();
    } catch (FileNotFoundException ex) {
      ex.printStackTrace();
      System.exit(-1);
    } catch (IOException ex) {
      ex.printStackTrace();
      System.exit(-1);
    }
  }
}

System: setIn(InputStream in)

  
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintStream;
public class Main {
  public static void main(String[] args) throws IOException {
    PrintStream console = System.out;
    BufferedInputStream in = new BufferedInputStream(new FileInputStream("Redirecting.java"));
    PrintStream out = new PrintStream(new BufferedOutputStream(new FileOutputStream("test.out")));
    System.setIn(in);
    System.setOut(out);
    System.setErr(out);
    BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
    String s;
    while ((s = br.readLine()) != null)
      System.out.println(s);
    out.close(); 
    System.setOut(console);
  }
}

System: setOut(PrintStream err)

    
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.PrintStream;
import java.sql.Timestamp;
public class MainClass {
  public static void main(String[] args) {
    try {
      String FILE = "c:\\systemin.txt";
      FileOutputStream outStr = new FileOutputStream(FILE, true);
      PrintStream printStream = new PrintStream(outStr);
      System.setErr(printStream);
      Timestamp now = new Timestamp(System.currentTimeMillis());
      System.out.println(now.toString() + ": This is text that should go to the file");
      outStr.close();
      printStream.close();
    } catch (FileNotFoundException ex) {
      ex.printStackTrace();
      System.exit(-1);
    } catch (IOException ex) {
      ex.printStackTrace();
      System.exit(-1);
    }
  }
}

System: setProperty(String key, String value)

    
public class Main {
  public static void main(String[] args) {
    System.setProperty("password", "myPassword");
    System.out.println(System.getProperty("password"));
  }
}