Initialization.java

package ej2.item71;

// Initialization styles - Pages 282-284
public class Initialization {

    // Normal initialization of an instance field - Page 282
    private final FieldType field1 = computeFieldValue();

    // Lazy initialization of instance field - synchronized accessor - Page 282
    private FieldType field2;
    synchronized FieldType getField2() {
        if (field2 == null)
            field2 = computeFieldValue();
        return field2;
    }

    // Lazy initialization holder class idiom for static fields - Page 283
    private static class FieldHolder {
        static final FieldType field = computeFieldValue();
    }
    static FieldType getField3() { return FieldHolder.field; }


    // Double-check idiom for lazy initialization of instance fields - Page 283
    private volatile FieldType field4;
    FieldType getField4() {
        FieldType result = field4;
        if (result == null) {  // First check (no locking)
            synchronized(this) {
                result = field4;
                if (result == null)  // Second check (with locking)
                    field4 = result = computeFieldValue();
            }
        }
        return result;
    }

    // Single-check idiom - can cause repeated initialization! - Page 284
    private volatile FieldType field5;
    private FieldType getField5() {
        FieldType result = field5;
        if (result == null) 
            field5 = result = computeFieldValue();
        return result;
    }

    private static FieldType computeFieldValue() {
        return new FieldType();
    }
}

class FieldType { }