java 实现数组扩容与缩容案例

public static <T> T[] dilatationArray(T[] datas,int newlen) {
 //不能为负数
 newlen = newlen<0?0:newlen;
 //生成一个新数组，并copy原值到新数组
 return Arrays.copyOf(datas, newlen);
 }

package testpro; 
import java.util.Arrays; 
/**
 * 数组扩容缩容
 * 扩容之后扩容部分按照类型默认赋值为0，false或者null
 * @author Administrator
 *
 */
public class ArrayDilatation {
 public static void main(String[] args) {
 Student[] students = new Student[60];
 for (int i=0;i<students.length;i++) {
  System.out.println(students[i]);
  students[i] = new Student("Stu"+i,"Gen"+i,i);
  System.out.println(students[i]);
 }
 System.out.println(students);
 students = dilatationArray(students, 60);
 for (Student student : students) {
  System.out.println(student);
 }
 System.out.println(students); 
 }
 
 public static <T> T[] dilatationArray(T[] datas,int newlen) {
 //不能为负数
 newlen = newlen<0?0:newlen;
 //生成一个新数组，并copy原值到新数组
 return Arrays.copyOf(datas, newlen);
 }
}
 
class Student{
 private String name;
 private String gender;
 private int age;
 
 public String getName() {
 return name;
 }
 public void setName(String name) {
 this.name = name;
 }
 public String getGender() {
 return gender;
 }
 public void setGender(String gender) {
 this.gender = gender;
 }
 public int getAge() {
 return age;
 }
 public void setAge(int age) {
 this.age = age;
 }
 public Student(String name, String gender, int age) {
 super();
 this.name = name;
 this.gender = gender;
 this.age = age;
 }
 @Override
 public String toString() {
 return "Student [name=" + name + ", gender=" + gender + ", age=" + age + "]";
 }
}

/**
 * @author yinglongwu
 */
 //适用泛型
public interface Stack<E> {
 int getSize();
 boolean isEmpty();
 void push(E e);//入栈
 E pop();//出栈
 E peek();//查看栈顶元素
}

/**
 * @author yinglongwu
 */
//这里通过自定义的Array类里的方法实现Stack接口，进而形成这个ArrayStack，
//并且也可以自动扩容
public class ArrayStack<E> implements Stack<E> {
 //这个Array<E>是自己封装的
 Array<E> array;
 
 //有参构造
 public ArrayStack(int capacity) {
 array = new Array<>(capacity);
 }
 //无参构造
 public ArrayStack() {
 array = new Array<>();//使用Array类里的无参构造
 }
 
 //获取栈的最大容量
 public int getCapacity() {
 return array.getCapacity();//调用的方法也是自己封装的Array类里的方法
 }
 
 //对接口中的方法进行重写
 @Override
 public int getSize() {
 return array.getSize();
 }
 @Override
 public boolean isEmpty() {
 return array.isEmpty();
 }
 //入栈
 @Override
 public void push(E e) {
 array.addLast(e);
 }
 //出栈
 @Override
 public E pop() {
 return array.removeLast();
 }
 //查看栈顶元素
 @Override
 public E peek() {
 return array.getLast();
 }
 
 //对toString方法进行重写，方便输出栈的基本信息
 @Override
 public String toString() {
 StringBuilder res = new StringBuilder();
 res.append("Stack: ");
 res.append('[');
 for (int i = 0; i < array.getSize(); i++) {
  res.append(array.get(i));
  if (i != array.getSize()-1) {
  res.append(", ");
  }
 }
 res.append("] top");//表明右侧是栈顶
 return res.toString();
 }
}

/**
 * @author yinglongwu
 */
public class Main {
 public static void main(String[] args) {
 
 //测试class ArrayStack
 ArrayStack<Integer> stack = new ArrayStack<Integer>();//new ArrayStack<Integer>()里的Integer可写可不写
 
 //包装类和其对应的基本数据类型可以自动转换
 //将0到4入栈
 for (int i = 0; i < 5; i++) {
  stack.push(i);
  System.out.println(stack);
 }
 
 //出一次栈
 stack.pop();
 System.out.println(stack);
 } 
}