Here are examples of how to initialize variables of the object types in Java:. Variable Declaration And Initialization. Select Chapter. The identifier is the name of the variable. You can initialize the variable by specifying an equal sign and a value.
It can be done at the time of declaration. It can be done anywhere, only once with the final-identifier. Before initialization objects have null value and primitive types have default values such as 0 or false. Can be done in conjunction with declaration. A variable can be declared only once. It is used by the compiler to help programmers avoid mistakes such as assigning string values to integer variables.
Before reading or assigning a variable, that variable must have been declared. Declaration is not to declare "value" to a variable; it's to declare the type of the variable. However, it should be mentioned that "initialization" also has a more relaxed definition of "the first assignment to a variable", regardless of where it happens.
Here i can be "initialized" from two possible locations, by simple assignments. Because of that, if i was an array, you can't use the special array initializer shorthand syntax with this construct. Declaration: Declaration is when you declare a variable with a name, and a variable can be declared only once.
Initialization: Initialization is when we put a value in a variable, this happens while we declare a variable. Assignment: Assignment is when we already declared or initialized a variable, and we are changing the value. You can change value of the variable as many time you want or you need.
Declaration - When a variable is declared, it is telling the compiler to set aside a piece of memory and associate a name and a variable type with it. The compiler sees this and sets aside an address location for x and knows what methods it should use to perform operations on x different variable types will use different access operations. This way, when the compiler runs into the line.
It knows to put the integer value 8 not the floating point value 8 into the memory location also known as 'x'. Assignment - This is when you stuff a value into the previously declared variable. Assignment is associated with the 'equals sign'. In the previous example, the variable 'x' was assigned the value 8. Initialization - This is when a variable is preset with a value. There is no guarantee that a variable will every be set to some default value during variable declaration unless you explicitly make it so.
It can be argued that initialization is the first assignment of a variable, but this isn't entirely true, as I will explain shortly. A typical initialization is a blend of the variable declaration with an assignment as follows:. The distinction between initialization and assignment becomes more important when dealing with constants, such as this Otherwise, they can't be touched.
This is because constants are often located in program memory vs data memory, and their actual assignment is occurring at compile time vs run time. Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? However, this form of initialization has limitations because of its simplicity.
If initialization requires some logic for example, error handling or a for loop to fill a complex array , simple assignment is inadequate. Instance variables can be initialized in constructors, where error handling or other logic can be used. To provide the same capability for class variables, the Java programming language includes static initialization blocks.
Here is an example:. A class can have any number of static initialization blocks, and they can appear anywhere in the class body. The runtime system guarantees that static initialization blocks are called in the order that they appear in the source code. The advantage of private static methods is that they can be reused later if you need to reinitialize the class variable.
Normally, you would put code to initialize an instance variable in a constructor.
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