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Copy file name to clipboardExpand all lines: app/pages/learn/01_tutorial/01_your-first-java-app/03_writing-java-applications-with-eclipse.md
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id: first_app.eclipse
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title: Developing Java applications using the Eclipse IDE
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title: Building a Java Application in the Eclipse IDE
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slug: learn/eclipse
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type: tutorial
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category: start
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main_css_id: learn
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toc:
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- Introduction and Installation {intro}
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- Creating Java projects {creating}
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- Creating a Java Project {creating}
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- Content Assist {content_assist}
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- Dealing with compilation errors and warnings {errors}
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- Running a program {run}
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- Running Your Program {run}
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- Dealing With Compilation Errors and Warnings {errors}
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- Debugging {debugging}
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- Generating code {generating}
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- Generating Code {generating}
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- Refactoring {refactoring}
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- Summary {summary}
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description: "Installing and getting started with the Eclipse IDE for developing Java applications"
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The Eclipse IDE (or Eclipse for short) is a commonly used application that provides tooling that helps developers write, run and debug Java code. This article describes how to get started with Eclipse for developing Java applications.
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The easiest way to install Eclipse is to download and run the Eclipse installer from [this site](https://www.eclipse.org/downloads/packages/installer). This provides multiple options for packages to install. In most cases, `Eclipse IDE for Java Developers` is a good installation for Java development.
Upon selecting a workspace, it will show a Welcome screen presenting you with mutliple options. For example, there is an option giving you an interactive tutorial showing you how to create a simple Hello-World application.
This article will show you how to create Java projects manually so you can close the welcome-screen by clicking on the `Hide` button on the top right of the Welcome tab.
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<aid="creating"> </a>
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## Creating Java projects
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## Creating a Java Project
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After installing Eclipse you should have an empty workspace. In order to create a new Java project, click on the `File` toolbar in the top left corner of the Eclipse window and select `New` > `Java Project`.
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After installing Eclipse, you should have an empty workspace. In order to create a new Java project, click on the `File`-toolbar on the top left corner of the Eclipse window and select `New` > `Java Project`.
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[](/assets/images/eclipse/file_create_project.png)
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This will then open up a dialog that allows configuring information about the project. You will need to enter a name next to `Project name:` at the top. For example, you can choose the name `HelloWorld`. In the `Module` section at the bottom, disable the option `Create module-info.java file`. If necessary, it is possible to configure a custom Java installation in the `JRE` box.
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This will then open up a dialog window that allows you to configure your project. You will need to enter a name next to `Project name:` at the top. For example, you can choose the name `HelloWorld`. In the `Module` section at the bottom, disable the option `Create module-info.java file`. You can configure a custom Java installation (commonly referred to as the *JDK* or Java Development Kit) in the `JRE` box.
This creates a Java project that is shown on the left side of the Eclipse window. When expanding this project, there should be a folder named `src`. Java classes can be created inside this directory by right-clicking on it and selecting `New` > `Class`.
This opens a dialog similar to the project creation dialog. It allows specifying various options about the class you want to create. For now, you will need to enter a class name like `HelloWorld`. If you want to, you can also configure a package which can be used to group multiple classes together.
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Eclipse can help you write Java code by automatically completing parts of it. When pressing the key combination `Ctrl`+`Space` (or `⌘`+`Space` on macOS or `Alt`+`/` on chinese systems) while editing Java code, Eclipse automatically suggests ways to complete the code. These suggestions can be confirmed by pressing `Enter` or double-clicking on the suggestions.
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For example, typing `main` in a class followed by pressing `Ctrl`+`Space` suggests adding a main method.
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For example, typing `main` in a class followed by pressing `Ctrl`+`Space` suggests adding a main method.
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[](/assets/images/eclipse/content_assist_main.png)
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Inside methods, Eclipse can suggest changing `sysout` to a `System.out.println();` statement.
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[](/assets/images/eclipse/content_assist_sysout.png)
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Furthermore, it can complete class and method names.
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[](/assets/images/eclipse/content_assist_suggest_class.png)
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[](/assets/images/eclipse/content_assist_suggest_method.png)
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<aid="run"> </a>
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## Running Your Program
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In order to run a Java application, you first need to have a class with a `main` method. You can right-click the class in the package explorer or right-click in the editor where you are writing the code for the class and select `Run as` > `Java application`.
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[](/assets/images/eclipse/run_as_editor.png)
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[](/assets/images/eclipse/run_as_package_explorer.png)
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Alternatively, you can run the application using the Run [](/assets/images/eclipse/run_button.png) button in the toolbar. [](/assets/images/eclipse/run_buttons_toolbar.png)
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When running the program, Eclipse should show the output of the program in the `Console` view.
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[](/assets/images/eclipse/console_output.png)
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<aid="errors"> </a>
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## Dealing with compilation errors and warnings
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## Dealing with Compilation Errors and Warnings
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When Eclipse detects a compilation error, the relevant lines are underlined in red. When hovering over the line with the error or the error icon to the left of the said line, Eclipse provides information about what went wrong and also suggests how to fix the error. However, in many cases there are multiple ways to get rid of the error. You need to carefully check whether the suggestions are actually matching what you want to do. After all, IDEs cannot predict your intent.
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[](/assets/images/eclipse/compilation_error.png)
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Furthermore, Eclipse shows a list of errors in the `Problems` view. If this view is not displayed, it can be shown using the menu `Window` > `Show View` > `Problems`.
[](/assets/images/eclipse/problems_view.png)
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As with Errors, Eclipse can also detect code that compiles but likely contains some issues or is pointless. In this case, Eclipse will display a warning.
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[](/assets/images/eclipse/warning.png)
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[](/assets/images/eclipse/problems_view_warning.png)
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<aid="run"> </a>
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## Running a program
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In order to run a Java application, you first need to have a class with a `main` method. You can right-click the class in the package explorer or right-click in the editor where you are writing the code for the class and select `Run as` > `Java application`.
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[](/assets/images/eclipse/run_as_editor.png)
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[](/assets/images/eclipse/run_as_package_explorer.png)
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Alternatively, you can run the application using the Run [](/assets/images/eclipse/run_button.png) button in the toolbar. [](/assets/images/eclipse/run_buttons_toolbar.png)
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[](/assets/images/eclipse/warning.png)
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When running the program, Eclipse should show the output of the program in the `Console` view.
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[](/assets/images/eclipse/console_output.png)
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[](/assets/images/eclipse/problems_view_warning.png)
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<aid="debugging"> </a>
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## Debugging
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When a program doesn't do what you expect it to do, you might want to debug it. The process of debugging is explained in [this article](id:debugging). Eclipse provides a lot of functionality making it easy to debug Java applications.
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In order to debug an application, you need to set a breakpoint. When the program gets to executing the line with the breakpoint, it will temporarily stop ("suspend"), allow you to inspect its current state and step through the program. To set a breakpoint, you need to double-click on the area to the left of the line you want to suspend the program at. After doing that, a blue dot should appear there.
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[](/assets/images/eclipse/breakpoint.png)
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When running a program normally, it will ignore all breakpoints. For debugging, you need to run the program in debug mode. This can be done by clicking on the green button with the bug icon [](/assets/images/eclipse/debug_button.png) next to the run button or using `Debug As` > `Java Application`.
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[](/assets/images/eclipse/debug_button_in_toolbar.png)
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When the program execution gets to a breakpoint in debug mode, Eclipse will ask you to switch to the Debug perspective. This perspective gives you more information about the program you are currently debugging so you likely want to do this and click on the `Switch` button.
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[](/assets/images/eclipse/debug_perspective_switch.png)
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Upon opening the debug perspective, you should still see your code in the middle. However, there should be one line with a green background next to the breakpoint. This indicates the next line the program would execute. On the right side, you should see a `Variables` view containing a list of variables and their current values.
While the program is suspended, you can tell it how to continue executing using buttons in the toolbar at the top.
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[](/assets/images/eclipse/debug_toolbar_buttons.png)
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You can execute one line using `Step Over`[](/assets/images/eclipse/debug_step_over.png) (`F6`), go into a method using `Step Into`[](/assets/images/eclipse/debug_step_into.png) (F5) or continue executing the program until the next breakpoint with `Resume`[](/assets/images/eclipse/debug_resume.png) (`F8`).
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<aid="generating"> </a>
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## Generating code
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## Generating Code
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Sometimes you might need to write repetitive code that doesn't contain much business logic and can be generated using information from existing code. An example of this is getters/setters or `equals`/`hashCode`/`toString` methods which typically just need to access some fields. While it is often preferable to use [records](/learn/records), Eclipse allows comes with functionality to generate these pieces of repetitive code.
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```
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When right-clicking in that class, there is an option called `Source` providing various ways to generate code. Here, we can select `Generate Getters and Setters...` in order to generate accessor methods for the fields in the `Person` class.
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[](/assets/images/eclipse/context_generate_getters_setters.png)
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This option should open up a new window allowing us to configure which fields we want to generate accessors for. In order to create accessors for all fields, use the `Select All` button. and click `Generate` on the bottom right.
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This option should open up a new window allowing us to configure which fields we want to generate accessors for. In order to create accessors for all fields, use the `Select All` button. and click `Generate` on the bottom right.
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[](/assets/images/eclipse/getter_setter_modal.png)
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After doing this, the class should look as follows:
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Another method that is often generated is `toString()` which returns a `String` representation of the object.
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To generate that method, select `Generate toString()...` in the `Source` menu.
As before, this opens a window allowing to specify options on how exactly the code should be generated.
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[](/assets/images/eclipse/tostring_options.png)
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Using the `Generate` button, Eclipse generates the `toString` method as it did with the other methods before.
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## Refactoring
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When working on Java applications, it is often necessary to change existing code in various ways while preserving functionality. Eclipse supports developers doing that by providing various refactoring options. An example of that is renaming class, methods or fields. This can be done by clicking on a class, method or variable name, right-clicking and selecting `Refactor` > `Rename`.
It is then possible to change to name to something different and confirming it using the `Enter` key. This also updates all references to the renamed element.
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[](/assets/images/eclipse/rename_box.png)
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[](/assets/images/eclipse/rename_different_text.png)
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