Java System.clearProperty() – Examples

In this tutorial, we will learn about the Java System.clearProperty() function, and learn how to use this function to remove a system property, with the help of examples.

clearProperty(String key)

System.clearProperty() removes the system property indicated by the specified key and returns the value for the key, that is removed.

If there is no property specified by the key, clearProperty() returns null.

Syntax

The syntax of clearProperty() function is

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clearProperty(String key)

where

ParameterDescription
keyThe name of the system property to be removed.

Returns

The function returns static String.

Example 1 – clearProperty(key)

In this example, we will clear the property identified by the key java.class.path using clearProperty() method. We will also print the value returned by this method.

Java Program

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public class Example {
	public static void main(String args[]) {
		String key = "java.class.path";
		
		System.out.println("Before clearProperty() = " + System.getProperty(key));
		
		String returnedValue = System.clearProperty(key);
		System.out.println("Returned Value         = " + returnedValue);
		
		System.out.println("After  clearProperty() = "+System.getProperty(key));
	}
}

Output

Before clearProperty() = C:\workspace\eclipse\JavaTutorial\bin;
Returned Value         = C:\workspace\eclipse\JavaTutorial\bin;
After  clearProperty() = null

Example 2 – clearProperty(key) – Key not present

In this example, we will clear the property identified by the key java.class.xyz using clearProperty() method. Since java.class.xyz is not a valid property, clearProperty() returns null.

Java Program

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public class Example {
	public static void main(String args[]) {
		String key = "java.class.xyz";
		
		System.out.println("Before clearProperty() = " + System.getProperty(key));
		
		String returnedValue = System.clearProperty(key);
		System.out.println("Returned Value         = " + returnedValue);
		
		System.out.println("After  clearProperty() = "+System.getProperty(key));
	}
}

Output

Before clearProperty() = null
Returned Value         = null
After  clearProperty() = null

Example 3 – clearProperty(key) – Empty Key

In this example, we will provide an empty key to clearProperty() method. clearProperty() should throw java.lang.IllegalArgumentException.

Java Program

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public class Example {
	public static void main(String args[]) {
		String key = "";
		System.clearProperty(key);
	}
}

Output

Exception in thread "main" java.lang.IllegalArgumentException: key can't be empty
	at java.base/java.lang.System.checkKey(Unknown Source)
	at java.base/java.lang.System.clearProperty(Unknown Source)
	at Example.main(Example.java:4)

Example 4 – clearProperty(key) – Null Key

In this example, we will provide a null value for key to clearProperty() method. clearProperty() should throw java.lang.NullPointerException.

Java Program

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public class Example {
	public static void main(String args[]) {
		String key = null;
		System.clearProperty(key);
	}
}

Output

Exception in thread "main" java.lang.NullPointerException: key can't be null
	at java.base/java.lang.System.checkKey(Unknown Source)
	at java.base/java.lang.System.clearProperty(Unknown Source)
	at Example.main(Example.java:4)

Conclusion

In this Java Tutorial, we have learnt the syntax of Java System.clearProperty() function, and also learnt how to use this function with the help of examples.