In Java, a layout manager is responsible for laying out components within a container. It provides a way to automatically arrange components based on their preferred size and the available space. Layout managers are used in Graphical User Interface (GUI) programming to create consistent and well-organized interfaces that look good on different screen sizes and resolutions.

Java provides several layout managers that can be used for different purposes, including:

1. FlowLayout - arranges components in a row, wrapping to the next row if necessary.
2. BorderLayout - arranges components in a five-region layout: north, south, east, west, and center.
3. GridLayout - arranges components in a grid of rows and columns.
4. CardLayout - allows multiple components to be stacked on top of each other, with only one visible at a time.
5. BoxLayout - arranges components in a row or column, and allows for flexible resizing of components.
6. GridBagLayout - arranges components in a grid, with each component having its own constraints for how it should be placed and sized.
7. GroupLayout - a flexible layout manager that allows for precise control over component positioning and sizing.

Layout managers are used in combination with containers, such as JFrame, JPanel, and JDialog, to create the desired layout for a GUI. The container's layout manager can be set using the setLayout() method. For example, to set a JFrame's layout manager to BorderLayout, you can do:

JFrame frame = new JFrame();
frame.setLayout(new BorderLayout());

Once the layout manager is set, you can add components to the container using methods such as add(), which will automatically arrange the components according to the layout manager's rules.

Layout managers can also be customized by setting properties and constraints on individual components. For example, in GridBagLayout, each component can be given a GridBagConstraints object that specifies how it should be placed and sized within the grid.

Overall, layout managers are an essential part of GUI programming in Java, and using the right layout manager for the job can make a big difference in the appearance and usability of an application's interface.