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Java Program to open the Command Prompt and Insert commands
This article uses various approaches for selecting the commands inserted in the opened command window through the Java code. The command window is opened by using ‘cmd’. Here, the methods of doing the same are specified using Java code. The Command window is first opened using the Java program. It is opened as a child process. If the java program is run in an existing cmd window, another one is opened as a new process. Further, different types of commands are inserted and executed in that opened command window via the java code.
These programs may not work in online programming environments. The details of how to run these programs by using javac and java commands are given in detail in this article, in the output section.
Algorithm
Step 1 − Using Java code open the CMD window.
Step 2 − Select the command to be executed. The selected command is used as a text String.
Step 3 − Execute the selected command in the opened CMD window through the Java program.
Step 4 − See the result.
Multiple Approaches
For these programs, the choice of commands is done using two different approaches.
By Using Commands that change the property of the cmd window.
By Using Executable Commands
Let’s see the program along with its output one by one.
First, the java code is given to start the new CMD window.
Java Code (to start the new CMD window)
public class cmdprog1 {
public static void main(String[] args) {
System.out.println("Opening cmd window");
try{
// cmd is a command that opens the command window
//CMD /C is used to run commands and then terminate the existing window while CMD /K will run the command and then it returns you to the given prompt. Runtime.getRuntime().exec(new String[] {"cmd", "/K", "Start"});
// the following line can also be used.....
//Runtime.getRuntime().exec(new String[] {"cmd", "/C", "Start"});
}
catch (Exception e){
System.out.println("Error: " + e);
}
}
}
Output
C:\java\javaprgstu>javac cmdprog1.java C:\java\javaprgstu>java cmdprog1 Opening cmd window C:\java\javaprgstu>
Approach-1: By Using Commands that change the property of the cmd window.
In this approach, two different examples are used.
Example 1: Change the Title of the CMD window while opening it.
Example 2: Change the background and foreground color of the CMD window while opening it.
Example 1: Change the Title of the CMD window while opening it.
Program
public class cmdprog22 {
public static void main(String[] args) {
String command_to_playwith =" title 'The New Title of the New Command Window' ";
System.out.println("Opening cmd window");
try {
String command = "cmd /c" + " start" + command_to_playwith;
//Starting the new child process
Process childprocess11 = Runtime.getRuntime().exec(command);
System.out.println("The child process is Alive: " + childprocess11.isAlive());
System.out.println();
}
catch (Exception e){
System.out.println("Error: " + e);
}
}
}
Output
C:\java\javaprgstu>javac cmdprog22.java C:\java\javaprgstu>java cmdprog22 Opening cmd window The child process is Alive: true
Example 2: Changes the background and foreground color of the CMD window while opening it.
public class cmdprog55 {
public static void main(String[] args) {
//the following command will change the color of the cmd window. First the number for bg color and then the number for fg color is added.
// 4 means red color and 0 means black color
String command_to_playwith =" COLOR 40";
System.out.println("Opening cmd window");
try {
String command = "cmd /c" + " start" + command_to_playwith;
// starting the child process ....
Process childprocess11 = Runtime.getRuntime().exec(command);
System.out.println("The child process is Alive: " + childprocess11.isAlive());
System.out.println();
}
catch (Exception e){
System.out.println("Error: " + e);
}
}
}
Output (Approach 1: Example 2)
C:\java\javaprgstu>javac cmdprog55.java C:\java\javaprgstu>java cmdprog55 Opening cmd window The child process is Alive: true
Approach-2: By Using the executable commands
The new cmd window is opened as the child process. The inserted command results will be seen in the new cmd window only. In this approach, three different examples are used.
Example 1 Display the message in the opened CMD window.
Example 2 Show the contents of a txt file.
Example 3 Show the folder contents in a wide format.
Example 1: Display the message in the opened CMD window.
public class cmdprog44 {
public static void main(String[] args) {
// The following command will display the message specified.
String command_to_playwith =" ECHO 'Hi! Lets check the cmd commands ....'";
System.out.println("Opening cmd window");
try {
String command = "cmd /c" + " start" + command_to_playwith;
// starting the child process....
Process childprocess11 = Runtime.getRuntime().exec(command);
System.out.println("The child process is Alive: " + childprocess11.isAlive());
System.out.println();
}
catch (Exception e){
System.out.println("Error: " + e);
}
}
}
System.out.println("Opening cmd window");
try {
String command = "cmd /c" + " start" + command_to_playwith;
// starting the child process ....
Process childprocess11 = Runtime.getRuntime().exec(command);
System.out.println("The child process is Alive: " + childprocess11.isAlive());
System.out.println();
}
catch (Exception e){
System.out.println("Error: " + e);
}
Output (Approach 2: Example 1)
C:\java\javaprgstu>javac cmdprog44.java C:\java\javaprgstu>java cmdprog44 Opening cmd window The child process is Alive: true
Example 2: Show the contents of a txt file.
public class cmdprog33 {
public static void main(String[] args) {
//The following command is the command that is needed to see the contents of the given text file
String command_to_playwith =" TYPE testfile.txt";
System.out.println("Opening cmd window");
try {
String command = "cmd /c" + " start" + command_to_playwith;
//Starting the new child process
Process childprocess11 = Runtime.getRuntime().exec(command);
System.out.println("The child process is Alive: " + childprocess11.isAlive());
System.out.println(" Now showing the content of testfile.txt ....\n");
}
catch (Exception e){
System.out.println("Error: " + e);
}
}
}
Output
C:\java\javaprgstu>javac cmdprog33.java C:\java\javaprgstu>java cmdprog33 Opening cmd window The child process is Alive: true Now showing the content of testfile.txt ...
Example 3: Show the folder contents in a wide format.
public class cmdprog66 {
public static void main(String[] args) {
// The following command will display the specified directory in wide format
String command_to_playwith =" dir .\applettest /W";
System.out.println("Opening cmd window");
try {
String command = "cmd /c" + " start" + command_to_playwith;
//Starting the new child process
Process childprocess11 = Runtime.getRuntime().exec(command);
System.out.println("The child process is Alive: " + childprocess11.isAlive());
System.out.println(" Now showing the directory in wide format ....\n");
}
catch (Exception e){
System.out.println("Error: " + e);
}
}
}
Output
C:\java\javaprgstu>javac cmdprog66.java C:\java\javaprgstu>java cmdprog66 Opening cmd window The child process is Alive: true Now showing the directory in wide format ...
Conclusion
In this article, we explored different commands to be inserted into the cmd window after opening it through the java program. The selection of commands is done based on the different categories. The first set of commands changes the properties of the command window while opening it and the second set of commands is used to show results in the opened command window after it is displayed. In both cases, the new cmd window is opened as a child process.
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