【我的Java笔记】增强for循环 & ArrayList集合储存自定义对象并遍历的五种方法
增强for循环
1.增强for循环的作用：
在集合中，增强for循环的作用是用来代替迭代器
2.优点：书写格式简单，代码量少
3.弊端：遍历数组或集合的时候，数组对象或者集合对象不能为null（需加上非空判断）
注：在Java中，只要是对象，那么一定要给对象做非空判断，避免出现空指针异常
4.书写格式：
for(数组或者集合中的数据类型 变量名：数组或者集合对象)｛
变量的输出；
｝
例：
import java.util.ArrayList;
public class Test2 {
public static void main(String[] args) {
//创建ArrayList集合对象
ArrayList al = new ArrayList();
//给集合中添加元素
al.add("hello");
al.add("world");
al.add("java");
//给集合对象进行非空判断
if(al!=null) {
//使用增强for循环遍历集合
for(String str:al) {
System.out.println(str);
}
}
}
} 
ArrayList集合储存自定义对象并遍历的五种方法
1.使用集合遍历（toArray()方法）：
import java.util.ArrayList;
//测试类
public class StudentTest {
public static void main(String[] args) {
//创建学生类对象
Student s1 = new Student("国际米兰",14);
Student s2 = new Student("罗马",56);
Student s3 = new Student("贝尔格莱德",45);
//创建ArrayList集合对象
ArrayList al = new ArrayList();
al.add(s1);
al.add(s2);
al.add(s3);
//使用toArray()方法将集合转为数组
Object [] obj = al.toArray();
//遍历数组
for(int i=0;i 
2.Collection集合的迭代器进行集合遍历（Iterator iterator()方法）
import java.util.ArrayList;
import java.util.Iterator;
//测试类
public class StudentTest {
public static void main(String[] args) {
System.out.println("使用Collection集合的迭代器Iterator iterator()方法进行集合遍历的结果：");
//创建学生类对象
Student s1 = new Student("国际米兰",14);
Student s2 = new Student("罗马",56);
Student s3 = new Student("贝尔格莱德",45);
//创建ArrayList集合对象
ArrayList al = new ArrayList();
al.add(s1);
al.add(s2);
al.add(s3);
//获取迭代器对象
Iterator it = al.iterator();
while(it.hasNext()) {
Student s = it.next();
System.out.println(s);
}
}
}
//学生类
class Student{
private String name;
private int age;
public Student() {
super();
}
public Student(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "["+name+","+age+"]";
}
} 
3.List集合的迭代器进行遍历（ListIterator listIterator()方法）
import java.util.ArrayList;
import java.util.ListIterator;
//测试类
public class StudentTest {
public static void main(String[] args) {
System.out.println("使用List集合的迭代器ListIterator listIterator()方法进行集合遍历的结果：");
//创建学生类对象
Student s1 = new Student("国际米兰",14);
Student s2 = new Student("罗马",56);
Student s3 = new Student("贝尔格莱德",45);
//创建ArrayList集合对象
ArrayList al = new ArrayList();
al.add(s1);
al.add(s2);
al.add(s3);
//获取迭代器对象
ListIterator it = al.listIterator();
while(it.hasNext()) {
Student s = it.next();
System.out.println(s);
}
}
}
//学生类
class Student{
private String name;
private int age;
public Student() {
super();
}
public Student(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "["+name+","+age+"]";
}
} 
4.普通for循环遍历集合（size() 和 get(int index) 方法相结合）
import java.util.ArrayList;
//测试类
public class StudentTest {
public static void main(String[] args) {
System.out.println("使用普通for循环方法进行集合遍历的结果：");
// 创建学生类对象
Student s1 = new Student("国际米兰", 14);
Student s2 = new Student("罗马", 56);
Student s3 = new Student("贝尔格莱德", 45);
// 创建ArrayList集合对象
ArrayList al = new ArrayList();
al.add(s1);
al.add(s2);
al.add(s3);
for (int i = 0; i < al.size(); i++) {
Student s = al.get(i);
System.out.println(s);
}
}
}
// 学生类
class Student {
private String name;
private int age;
public Student() {
super();
}
public Student(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "[" + name + "," + age + "]";
}
} 
5.增强for循环进行集合的遍历
import java.util.ArrayList;
//测试类
public class StudentTest {
public static void main(String[] args) {
System.out.println("使用增强for循环方法进行集合遍历的结果：");
// 创建学生类对象
Student s1 = new Student("国际米兰", 14);
Student s2 = new Student("罗马", 56);
Student s3 = new Student("贝尔格莱德", 45);
// 创建ArrayList集合对象
ArrayList al = new ArrayList();
al.add(s1);
al.add(s2);
al.add(s3);
//使用增强for循环行进遍历
for (Student s:al) {
System.out.println(s);
}
}
}
// 学生类
class Student {
private String name;
private int age;
public Student() {
super();
}
public Student(String name, int age) {
super();
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "[" + name + "," + age + "]";
}
} 