The following partial disassembly reveals the bytecode instruction sequence for the () method. The type is represented by a single letter: I for int and D for double. The Descriptor line identifies the JVM's type descriptor for the field. The following partial disassembly reveals the stored information for the x, temp, and y fields: Field #1 The angle brackets prevent a name conflict: you cannot declare a () method in source code because the characters are illegal in an identifier context.Īfter loading a class, the JVM calls this method before calling main() (when main() is present). When compiling class initializers and class initialization blocks, the Java compiler stores the compiled bytecode (in top-down order) in a special method named (). Initializing arrays of sine and cosine values class Graphics When the class loads, these statements are executed. You can use a class initialization block for this task.Ī class initialization block is a block of statements preceded by the static keyword that's introduced into the class's body. You will do this after a class has been loaded and before any objects are created from that class (assuming that the class isn't a utility class). In some cases you may want to perform complex class-based initializations. (It would also output this message if y wasn't explicitly initialized.) Class initialization blocks This is because source code is compiled from the top down, and the compiler hasn't yet seen y. The compiler will report illegal forward reference when it encounters static int x = y. Attempting to reference a subsequently declared field class SomeClass The Java compiler outputs illegal forward reference when it encounters this scenario. However, the reverse is not legal: you cannot initialize a class field to the value of a subsequently declared class field. Referencing a previously declared field class SomeClass For example, Listing 3 initializes y to x's value. When initializing a class field, it's legal to initialize it to the value of a previously initialized class field. Variable st stores a reference to a String object that contains abc. Each variable stores the value directly, with the exception of st. Initializing class fields to explicit values class SomeClassĮach assignment's value must be type-compatible with the class field's type. However, you can also explicitly initialize class fields by directly assigning values to them, as shown in Listing 2. The previous class fields were implicitly initialized to zero.
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