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load a reference onto the stack from a local variable #index: aload_0 2a 0010 1010 → objectref load a reference onto the stack from local variable 0 aload_1 2b 0010 1011 → objectref load a reference onto the stack from local variable 1 aload_2 2c 0010 1100 → objectref load a reference onto the stack from local variable 2 aload_3 2d 0010 1101
In object-oriented computer programming, a null object is an object with no referenced value or with defined neutral (null) behavior.The null object design pattern, which describes the uses of such objects and their behavior (or lack thereof), was first published as "Void Value" [1] and later in the Pattern Languages of Program Design book series as "Null Object".
Java bytecode is the instruction set of the Java virtual machine (JVM), the language to which Java and other JVM-compatible source code is compiled. [1] Each instruction is represented by a single byte, hence the name bytecode, making it a compact form of data.
A method returns to the code that invoked it when it completes all the statements in the method, reaches a return statement, or throws an exception, whichever occurs first. You declare a method's return type in its method declaration. Within the body of the method, you use the return statement to return the value.
The return statement is used to end method execution and to return a value. A value returned by the method is written after the return keyword. If the method returns anything but void, it must use the return statement to return some value.
With automatic unboxing the compiler automatically supplies the extra source code that retrieves the value out of that object, either by invoking some method on that object, or by other means. For example, in versions of Java prior to J2SE 5.0, the following code did not compile:
For object values, the reference cannot change. This allows the Java compiler to "capture" the value of the variable at run-time and store a copy as a field in the inner class. Once the outer method has terminated and its stack frame has been removed, the original variable is gone but the inner class's private copy persists in the class's own ...
Each of these reference types extends the Reference class, which provides the get() method to return a strong reference to the referent object (or null if the reference has been cleared or if the reference type is phantom), and the clear() method to clear the reference. The java.lang.ref also defines the class ReferenceQueue, which can be used ...