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Access Modifiers

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Access modifiers: package-default, public
Non-access modifiers: abstract (cannot be static/final)

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Constructors

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Access modifiers: private, package-default, protected, public
Non-access modifiers: none are allowed

• No return type allowed.

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Blocks

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Access modifiers: package-default
Non-access modifiers: static or none

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Members

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Access modifiers: private, package-default, protected, public
Non-access modifiers: static, final, transient, volatile

• If final must be initialized and cannot be volatile.

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Methods

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Access modifiers: private, package-default, protected, public
Non-access modifiers: static, abstract, final, native, strictfp

native:

• Cannot have body code, looks like abstract method e.g. public native void method();
• Must have return type void;
• Cannot be strictfp;
• Can have any other access and non-access modifier type.

abstract:

• Only the access modifier can be set: package-default, protected, public (NOT private);
• Cannot set non-access modifiers: final, native, strictfp, synchronized;
• Has no body e.g. public void abstract method();

static/final:

• Only non-abstract methods can be static/final;
• It does not make sense that abstract methods are static/final as static/final methods cannot be overridden. The purpose of abstract classes is that they are implemented/overwritten.

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Behaviours

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• Abstract classes cannot be instantiated.
• Can be subclassed (extended) – subclasses must implement all abstract methods.
• Subclass inherits non-abstract methods/members which can be overridden.
• Implemented methods in subclasses can be synchronized even though the parent abstract method cannot be set as synchronized.