Variables
Static variables are initialized only once.
/**
* Static variables are initialized only once.
*
* A static class variable is common to all objects created with that class.
* It can be called without object instantiation.
*/
package com.minte9.oop.static_keyword;
public class Variables {
public static void main(String[] args) {
A a1 = new A();
A a2 = new A();
System.out.println(a1.getCount()); // 2 (not 1)
System.out.println(a2.getCount()); // 2
}
}
class A {
private static int count;
public A() {
count++;
}
public int getCount() {
return count;
}
}
Methods
Static methods can't be access from a class instances.
/**
* Static methods belong to the class and not every instance of the class.
* Example: Java.lang.Math has a round() static method.
*/
package com.minte9.oop.static_keyword;
public class Methods {
public static void main(String[] args) {
System.out.println(
Math.round(42.2) // 42
);
System.out.println(
Methods.myRound(33.5) // 34
);
// Math m = new Math(); // Error: private access
}
private static long myRound(Double n) {
return Math.round(n);
}
}
Classes
Only nested classes can be static.
/**
* Static classes
*
* Only nested classes can be static
* You can use the nested class without an instance for outer class
*/
package com.minte9.oop.static_keyword;
public class Classes {
static int a = 10;
public static void main(String[] args) {
InnerClass.run(); // 10
}
static class InnerClass {
public static void run() {
System.out.println(a); // field from Outer Class
}
}
}
Last update: 531 days ago
