finaldata.java

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//: FinalData.java
// The effect of final fields

class Value {
	int i = 1;
}

public class FinalData {
	// Can be compile-time constants
	final int i1 = 9;
	static final int I2 = 99;
	// Typical public constant:
	public static final int I3 = 39;
	// Cannot be compile-time constants:
	final int i4 = (int)(Math.random()*20);
	static final int i5 = (int)(Math.random()*20);

	Value v1 = new Value();
	final Value v2 = new Value();
	static final Value v3 = new Value();
	//! final Value v4;				// Pre-Java 1.1 error; no initializer

	// Arrays:
	final int[] a = {1,2,3,4,5,6};

	public void print(String id) {
		System.out.print(
			id + ": " + "i4 = " + i4 + ", i5 = " + i5);
	}
	public static void main(String[] args) {
		FinalData fd1 = new FinalData();
		//! fd1.i1++;				//	Error: can't change value
		fd1.v2.i++;					//	Object isn't constant!
		fd1.v1 = new Value();		//	OK -- not final
		for ( int i = 0; i< fd1.a.length; ++i )
			fd1.a[i]++;				//	Object isn't constant!
		//! fd1.v2 = new Value();	//	Error: Can't
		//! fd1.v3 = new Value();	//	change handle
		//! fd1.a = new int[3];
	
		fd1.print("fd1");
		System.out.println("Creating new FinalData");
		FinalData fd2 = new FinalData();
		fd1.print("fd1");
		fd2.print("fd2");
	}
}