The null
Keyword in Java
The “null” keyword in the Java programming language represents that a reference variable does not reference any object.
Indicates Uninitialized or Empty Reference
Using “null” for a reference variable indicates that this variable does not reference any object, meaning it is uninitialized or an empty reference.
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String myString = null; // Declare a string reference variable and initialize it to null
In this case, the
myString
reference variable is declared but does not reference any string object. To use this reference variable, you need to assign it to an actual string object.Null Reference Check
In programming, you need to check whether a reference variable is null to avoid a null pointer exception.
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7if (myString != null) {
// Perform operations because myString reference is not null
System.out.println(myString.length());
} else {
// Handle the null reference case
System.out.println("myString is null");
}Object Destruction and Garbage Collection
In Java, the lifecycle of objects is managed by the garbage collector. When no references point to an object, it becomes garbage and will eventually be collected by the garbage collector.
Setting a reference variable to null explicitly releases the reference to the object, which can expedite garbage collection.
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4MyClass obj = new MyClass();
// Use the obj object...
obj = null; // Set obj to null, releasing the reference to the original object
// The original object now has no references and will be garbage collectedNote: Setting a reference variable to null does not immediately destroy the object; rather, it tells the garbage collector that the reference is no longer in use. The garbage collector will collect objects that are no longer referenced at an appropriate time.