This method requires a body instead of a semicolon

The reason for the error "This method requires a body instead of a semicolon" is same as described in the post missing method body, or declare abstract.

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is not abstract and does not override abstract method

See the code below:

import javax.swing.JFrame;
import javax.swing.JButton;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class MyFrame extends JFrame implements ActionListener{
private JButton exitButton = new JButton("Exit");
public MyFrame()
{
Container container = getContentPane();
container.setLayout(new FlowLayout());
container.add(exitButton);
  exitButton.addActionListener(this);
setSize(300,200);
}
}

If this code is compiled, we will see the error "MyFrame is not abstract and does not override abstract method actionPerformed(java.awt.event.ActionEvent) in java.awt.event.ActionListener"

Why? When we implement an interface(ActionListener in this example) or extend an abstract class in a concrete class, we must override the abstract method(s). In the above example we have implemented ActionListener but have not overridden the abstract method actionPerformed.

The correct code of the above is:

import javax.swing.JFrame;
import javax.swing.JButton;
import java.awt.Container;
import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

public class MyFrame extends JFrame implements ActionListener
{
private JButton exitButton = new JButton("Exit");
public MyFrame()
{
Container container = getContentPane();
container.setLayout(new FlowLayout());
container.add(exitButton);
exitButton.addActionListener(this);
setSize(300,200);
}
public void actionPerformed(ActionEvent ae)
{
System.exit(0);
}
}

Sometimes it happens that we override the abstract method with wrong name spelling or wrong signature, then also we see the same error message. Note that Java is a case sensitive language; most often we write the method name with wrong case (example, actionperformed/ActionPerformed instead of actionPerformed) and see this error message.

For implementing an interface or extending an abstract class, we must override all of the abstract methods (if more than one), though we do not need all. For example, if we implement KeyListener we must override each of the three abstract methods keyPressed, keyTyped and keyReleased though we may not need all of them. In that case, method body can be kept blank. Instead of interface, we can use adapter class (if available) to get rid of overriding all abstract methods.

In summary, override the abstract method with correct name spelling and signature to remove the error.

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illegal combination of modifiers: abstract and static

An abstract method cannot be static because the abstract method must be overridden i.e, body of the abstract method must be defined before invocation.

See the wrong code below:

public abstract class Employee
{
public static abstract double earnings(); // error
}

Here the abstract method earnings() is declared as static. An abstract method must be non-static. So the correct code is:

public abstract class Employee
{
public abstract double earnings(); // no error now
}

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missing method body, or declare abstract

If we put a ; (semicolon) after the method header (i.e., before starting the method body) when we are defining a concrete method (which method has body) then we will see “missing method body, or declare abstract”. Another reason is if we don’t write the keyword ‘abstract’ for an abstract method (a method without body), we’ll also see this message.
To resolve the problem we must remove the ; (semicolon) from the header of the concrete method or if it is an abstract method the keyword ‘abstract’ must be written in the method header.

Here is an example of this error:

public abstract class MissingMethodBodyOrDeclareAbstract
{
public void display(String message);
{
System.out.println(message);
}
public void display();
}

Here, a ; (semicolon) is given after the method header of the first display method (with parameter). And for the second display method, keyword ‘abstract’ is not stated in the header and it doesn’t have any body also. Here it is to be noted that if a class contains an abstract method, the class must also be abstract.

The correct code is:

public abstract class MissingMethodBodyOrDeclareAbstractSolution
{
public void display(String message)
{
System.out.println(message);
}
public abstract void display();
}

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