![Declaração e Inicialização de Variáveis em Java](https://img.php.cn/upload/article/000/000/000/172103265235117.jpg)
Variable Declaration
- All variables must be declared before use.
- Necessary for the compiler to know the data type of the variable.
- Allows strict type checking.
Variable Initialization
- It is recommended to give the variable a value before using it.
Can be done by:
- Assignment Instruction.
- Initial value in the declaration.
int count = 10; // valor inicial
char ch = 'X'; // inicializa com 'X'
float f = 1.2F; // inicializa com 1.2
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- You can initialize variables of the same type in a comma-separated list.
Dynamic Startup
- Variables can be dynamically initialized using valid expressions.
double volume = 3.1416 * radius * radius * height;
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Scope and Lifetime of Variables
- Variables can be declared within any block.
A block defines a scope:
- Determines the visibility and lifetime of variables.
- Variables within a scope cannot be seen outside of it.
Scopes can be nested:
- Variables in external scopes are visible in internal scopes.
- Variables in internal scopes are not visible in external scopes.
int x = 10;
if(x == 10) {
int y = 20;
System.out.println("x and y: " + x + " " + y);
x = y * 2;
}
System.out.println("x is " + x);
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Scope Rules and Peculiarities
for(int x = 0; x < 3; x++) {
int y = -1;
System.out.println("y is: " + y);
y = 100;
System.out.println("y is now: " + y);
}
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- In Java, variables in internal scopes cannot have the same name as variables in external scopes.
// Este programa não será compilado
int count;
for(count = 0; count < 10; count++) {
int count; // inválido
for(count = 0; count < 2; count++)
System.out.println("This program is in error!");
}
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Summary of Key Points
- Variables must be declared before use to enable type checking.
- Initialization can be done in declaration or dynamically.
- The scope of a variable determines where it can be accessed.
- Scopes can be nested and variables in the inner scope cannot have the same name as variables in the outer scope.
- The lifetime of a variable is confined to its scope.
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