Refactor VariableSizeLookaheadIterator

Previously, when referencing instance fields from readNextItem,
the fields wouldn't have been initialized yet on the first call to
readNextItem

brut.apktool.smali/dexlib2/src/main/java/org/jf/dexlib2/dexbacked/DexBackedClassDef.java

@@ -173,7 +173,7 @@ public class DexBackedClassDef extends BaseTypeReference implements ClassDef {
                             while (true) {
                                 if (++count > staticFieldCount) {
                                     instanceFieldsOffset = reader.getOffset();
-                                    return null;
+                                    return endOfData();
                                 }
 
                                 DexBackedField item = new DexBackedField(reader, DexBackedClassDef.this,
@@ -232,7 +232,7 @@ public class DexBackedClassDef extends BaseTypeReference implements ClassDef {
                             while (true) {
                                 if (++count > instanceFieldCount) {
                                     directMethodsOffset = reader.getOffset();
-                                    return null;
+                                    return endOfData();
                                 }
 
                                 DexBackedField item = new DexBackedField(reader, DexBackedClassDef.this,
@@ -301,7 +301,7 @@ public class DexBackedClassDef extends BaseTypeReference implements ClassDef {
                             while (true) {
                                 if (++count > directMethodCount) {
                                     virtualMethodsOffset = reader.getOffset();
-                                    return null;
+                                    return endOfData();
                                 }
 
                                 DexBackedMethod item = new DexBackedMethod(reader, DexBackedClassDef.this,
@@ -357,7 +357,7 @@ public class DexBackedClassDef extends BaseTypeReference implements ClassDef {
                         protected DexBackedMethod readNextItem(@Nonnull DexReader reader) {
                             while (true) {
                                 if (++count > virtualMethodCount) {
-                                    return null;
+                                    return endOfData();
                                 }
 
                                 DexBackedMethod item = new DexBackedMethod(reader, DexBackedClassDef.this,

brut.apktool.smali/dexlib2/src/main/java/org/jf/dexlib2/dexbacked/DexBackedMethodImplementation.java

@@ -76,7 +76,7 @@ public class DexBackedMethodImplementation implements MethodImplementation {
                     @Override
                     protected Instruction readNextItem(@Nonnull DexReader reader) {
                         if (reader.getOffset() >= endOffset) {
-                            return null;
+                            return endOfData();
                         }
 
                         Instruction instruction = DexBackedInstruction.readFrom(reader);

brut.apktool.smali/dexlib2/src/main/java/org/jf/dexlib2/dexbacked/util/DebugInfo.java

@@ -160,7 +160,7 @@ public abstract class DebugInfo implements Iterable<DebugItem> {
                         int next = reader.readUbyte();
                         switch (next) {
                             case DebugItemType.END_SEQUENCE: {
-                                return null;
+                                return endOfData();
                             }
                             case DebugItemType.ADVANCE_PC: {
                                 int addressDiff = reader.readSmallUleb128();

brut.apktool.smali/dexlib2/src/main/java/org/jf/dexlib2/dexbacked/util/VariableSizeLookaheadIterator.java

@@ -31,46 +31,32 @@
 
 package org.jf.dexlib2.dexbacked.util;
 
+import com.google.common.collect.AbstractIterator;
 import org.jf.dexlib2.dexbacked.DexBackedDexFile;
 import org.jf.dexlib2.dexbacked.DexReader;
 
 import javax.annotation.Nonnull;
 import javax.annotation.Nullable;
 import java.util.Iterator;
-import java.util.NoSuchElementException;
 
-public abstract class VariableSizeLookaheadIterator<T> implements Iterator<T> {
+public abstract class VariableSizeLookaheadIterator<T> extends AbstractIterator<T> implements Iterator<T> {
     @Nonnull private final DexReader reader;
 
-    private T cachedItem = null;
-
     protected VariableSizeLookaheadIterator(@Nonnull DexBackedDexFile dexFile, int offset) {
         this.reader = dexFile.readerAt(offset);
-        cachedItem = readNextItem(reader);
     }
 
     /**
-     * Reads the next item from reader. If the end of the list has been reached, it should return null.
+     * Reads the next item from reader. If the end of the list has been reached, it should call endOfData.
      *
-     * @return The item that was read, or null if the end of the list has been reached.
+     * endOfData has a return value of T, so you can simply {@code return endOfData()}
+     *
+     * @return The item that was read. If endOfData was called, the return value is ignored.
      */
     @Nullable protected abstract T readNextItem(@Nonnull DexReader reader);
 
     @Override
-    public boolean hasNext() {
+    protected T computeNext() {
-        return cachedItem != null;
+        return readNextItem(reader);
     }
-
-    @Override
-    @Nonnull
-    public T next() {
-        if (cachedItem == null) {
-            throw new NoSuchElementException();
-        }
-        T ret = cachedItem;
-        cachedItem = readNextItem(reader);
-        return ret;
-    }
-
-    @Override public void remove() { throw new UnsupportedOperationException(); }
 }