java实现B-Tree

package com.algorithm.tree;import java.lang.reflect.Array;import java.util.ArrayList;import java.util.Arrays;import java.util.Collections;import java.util.Iterator;import java.util.List;public class BTree<T extends Comparable<T>> {public int minDgree;public int keynum;public T[] key;public ArrayList<BTree<T>> child;public boolean isLeaf;public BTree(){}public BTree(T[] array,int minDegree){BTree<T> btree=new BTree<T>();btree.isLeaf=true;btree.minDgree=minDegree;btree.keynum=0;btree.key=(T[])Array.newInstance(array.getClass().getComponentType(), 2*minDegree-1);Arrays.fill(btree.key, 0); /*使用反射得到的数组填充一下再使用，省略此处会产生NullPointerException*/btree.child=new ArrayList<BTree<T>>(2*minDegree);/*Collections.fill(btree.child, null);使用此方法不会改变size()大小，换句话说此方法填充的元素数量取决于size()而不是capacity()!!!!*/for(int i=0;i<2*minDegree;i++){btree.child.add(null);}int i=1;for(T ele:array){btree=insert(btree,ele);System.out.println("初始化第"+i+++"个节点");keynum=btree.keynum;isLeaf=btree.isLeaf;key=btree.key;child=btree.child;this.minDgree=minDegree;}}public static <T extends Comparable<T>> void split(BTree<T> parent,int i){BTree<T> first=parent.child.get(i);BTree<T> second=new BTree<>();second.minDgree=parent.minDgree;second.isLeaf=first.isLeaf;second.key=(T[])Array.newInstance(parent.key.getClass().getComponentType(), 2*parent.minDgree-1);second.child=new ArrayList<BTree<T>>(2*parent.minDgree);for(int k=0;k<2*parent.minDgree;k++){second.child.add(null);}int j=parent.minDgree;int m=0;while(j<first.keynum){second.key[m]=first.key[j];second.child.set(m++, first.child.get(j++));}second.child.set(m, first.child.get(j));first.keynum=second.keynum=parent.minDgree-1;j=parent.keynum-1;while(j>=i){parent.key[j+1]=parent.key[j];if(j!=i) parent.child.set(j+1, parent.child.get(j));j--;}parent.key[i]=first.key[parent.minDgree-1];parent.keynum++;parent.child.set(i+1, second);System.out.println("fenliehou keynum"+parent.keynum+"zhiwei"+parent.key[i]+"i wei"+i);}public static <T extends Comparable<T>> BTree<T> insert(BTree<T> root,T ele){if(root==null) return null;if(root.keynum==(2*root.minDgree-1)){BTree newRoot=new BTree();newRoot.minDgree=root.minDgree;newRoot.isLeaf=false;newRoot.key=(T[])Array.newInstance(root.key.getClass().getComponentType(), Array.getLength(root.key));Arrays.fill(newRoot.key, 0);newRoot.keynum=0;newRoot.child=new ArrayList<T>(Array.getLength(root.key)+1);for(int i=0;i<2*newRoot.minDgree;i++){newRoot.child.add(null);}newRoot.child.set(0, root);split(newRoot,0);insertNonfull(newRoot,ele);return newRoot;}else{insertNonfull(root,ele);return root;}}public static <T extends Comparable<T>> void insertNonfull(BTree<T> p,T ele){T[] newArray=(T[])Arrays.copyOf(p.key, p.keynum);int i=Arrays.binarySearch(newArray, ele);int insertionPoint=-(i+1);if(i<0 && !p.isLeaf){if(p.child.get(insertionPoint).keynum==(2*p.minDgree-1)){split(p,insertionPoint);insertionPoint=ele.compareTo(p.key[insertionPoint])>0 ? (insertionPoint+1):insertionPoint;}insertNonfull(p.child.get(insertionPoint),ele);}if(i<0 && p.isLeaf){int j=p.keynum-1;while(j>=insertionPoint){p.key[j+1]=p.key[j];j--;}p.key[insertionPoint]=ele;System.out.println("cha ru ele"+ele+"wei zhi"+insertionPoint+"jie dian"+p+"keynum"+p.keynum);p.keynum++;}}public boolean search(T k){T[] array=Arrays.copyOf(key, keynum);int i=Arrays.binarySearch(array, k);/*NullPointerException null不能参与比较大小 */if(i>=0) return true;if(isLeaf) return false;int insertionPoint=-(i+1);return child.get(insertionPoint).search(k);}public void traverse(){int i;for(i=0;i<keynum;i++){if(child.get(i)!=null) child.get(i).traverse();System.out.print(key[i]+",");}if(child.get(i)!=null) child.get(i).traverse();}public static void main(String[] args){BTree<Integer> btree=new BTree<Integer>(new Integer[]{1,2,3,4,5,6,7,8,9,10,11,12,13},3);btree.traverse();boolean b1=btree.search(12);boolean b2=btree.search(49);System.out.println("\nb1 : "+b1+"   b2 : "+b2);}}

输出结果：

cha ru ele1wei zhi0jie diancom.algorithm.tree.BTree@17e121ckeynum0
初始化第1个节点
cha ru ele2wei zhi1jie diancom.algorithm.tree.BTree@17e121ckeynum1
初始化第2个节点
cha ru ele3wei zhi2jie diancom.algorithm.tree.BTree@17e121ckeynum2
初始化第3个节点
cha ru ele4wei zhi3jie diancom.algorithm.tree.BTree@17e121ckeynum3
初始化第4个节点
cha ru ele5wei zhi4jie diancom.algorithm.tree.BTree@17e121ckeynum4
初始化第5个节点
fenliehou keynum1zhiwei3i wei0
cha ru ele6wei zhi2jie diancom.algorithm.tree.BTree@1d6f122keynum2
初始化第6个节点
cha ru ele7wei zhi3jie diancom.algorithm.tree.BTree@1d6f122keynum3
初始化第7个节点
cha ru ele8wei zhi4jie diancom.algorithm.tree.BTree@1d6f122keynum4
初始化第8个节点
fenliehou keynum2zhiwei6i wei1
cha ru ele9wei zhi2jie diancom.algorithm.tree.BTree@7109c4keynum2
初始化第9个节点
cha ru ele10wei zhi3jie diancom.algorithm.tree.BTree@7109c4keynum3
初始化第10个节点
cha ru ele11wei zhi4jie diancom.algorithm.tree.BTree@7109c4keynum4
初始化第11个节点
fenliehou keynum3zhiwei9i wei2
cha ru ele12wei zhi2jie diancom.algorithm.tree.BTree@1385660keynum2
初始化第12个节点
cha ru ele13wei zhi3jie diancom.algorithm.tree.BTree@1385660keynum3
初始化第13个节点
1,2,3,4,5,6,7,8,9,10,11,12,13,
b1 : true   b2 : false