Static Field Summary

Class Fields (Static Fields)

• Fields associated with class rather than instances
• Declared using static keyword
• Shared across all instances of the class
• Can be accessed without creating class instance
• Example:

  // Universal field: PI
  class Math {
    public static final double PI = 3.141592653589793;
  }
  

Common Modifiers for Class Fields

• static: Makes field belong to class
• final: Makes field value unchangeable
• public: Makes field accessible outside class
• Common combination: public static final for defining globally accessible constants.

Accessing Class Fields

• Access through class name: Math.PI
• Example:

  public double getArea() {
    return java.lang.Math.PI * this.r * this.r;
  }
  

• Can use import statement to simplify access
• Example:

  import java.lang.Math;
  
  // Now can use Math.PI directly
  public double Circumference() {
    return Math.PI * this.r * 2;
  }
  

Instance Fields vs Class Fields

• Instance fields (non-static field):

  • Belong to specific object instances
  • Each object has its own separate copy of the field
  • Accessed through object reference

• Class fields (static field):

  • Belong to class itself
  • Single copy shared by all instances
  • Accessed through class name
  • Loaded into memory when class is loaded by JVM, even if no objects are created

Best Practices

• Use class fields for:
  • Constants
  • Values shared across all instances
  • Configuration parameters
  • Pre-computed values
• Make class fields final when possible
• Use meaningful names for constants
• Consider using existing constants (e.g., Math.PI)