Java -2
常用API
System
- 可以获取当前时间，以此计算运行代码的时间
- 也可以控制代码的结束
//获取当前时间点-毫秒 1970 1-1 8:00
long num = System.currentTimeMillis();
System.out.println(num);
//系统退出运行
System.exit(0);Runtime
获取操作系统的线程大小 能从操作系统最多获取多少内存大小 已经获取的获取的内存大小-M 剩下的内存大小 在固定时间关机与取消
//获取操作系统的线程大小
int nums = Runtime.getRuntime().availableProcessors();
System.out.println(nums);
//能从操作系统最多获取多少内存大小
long l = Runtime.getRuntime().maxMemory();
System.out.println(l / 1024 / 1024);
//已经获取的获取的内存大小
long L = Runtime.getRuntime().totalMemory();
System.out.println(L / 1024 / 1024);
//剩下的内存大小
long LL = Runtime.getRuntime().freeMemory();
System.out.println(LL / 1024 / 1024);
//在固定时间关机与取消
Runtime.getRuntime().exec("shutdown -s -t 3600");
Runtime.getRuntime().exec("shutdown -a");
System.exit(0);equals
import java.util.Objects;
public class Equals {
String name;
int age;
public Equals(String name, int age) {
this.name = name;
this.age = age;
}
public Equals() {
}
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 boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Equals equals = (Equals) o;
return age == equals.age && Objects.equals(name, equals.name);
}
@Override
public int hashCode() {
return Objects.hash(name, age);
}
}
public class BiEqual {
public static void main(String[] args) {
Equals a1 = new Equals("ax", 11);
Equals a2 = new Equals("ax", 11);
boolean w = a1.equals(a2);
System.out.println(w);
//这里的比较默认的是对象的地址，如果想要比较具体的参数值需重写
String s = "ax";
StringBuilder sb = new StringBuilder("ax");
boolean equals = s.equals(sb.toString());
boolean equals1 = s.equals(sb);
boolean equals2 = sb.equals(s);
System.out.println(equals);
System.out.println(equals1);
System.out.println(equals2);
//String中的String中的equals方法是先判断是否为字符串，如果不是字符串那再继续比较其他属性
//StringBuilder中没有重写特定的equals方法只能从obj中继承
//obj中equals比较的是对象的地址
}
}
Objects下的equqls可以有非空判断
clone
浅克隆与深克隆（在于引用数据类型数组的更改变化）
对象拷贝：clone方法是protected只可以在子类中被调用，在这里需要重写
并且java类中要继承Cloneable接口
该接口没有抽象方法，是一个标记性接口
Cloneable实现当前类可以被克隆，没有实现当前类的对象不可以被克隆
浅克隆，浅拷贝：
javabean类
public class CloneStudent implements Cloneable {
String name;
int age;
int[] arr;
public CloneStudent(String name, int age, int[] arr) {
this.name = name;
this.age = age;
this.arr = arr;
}
public CloneStudent() {
}
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;
}
public int[] getArr() {
return arr;
}
public void setArr(int[] arr) {
this.arr = arr;
}
public void getCloneArr() {
for (int j : arr) {
System.out.print(j + " ");
}
}
@Override
protected Object clone() throws CloneNotSupportedException {
return super.clone();
}
}
实现类
public class CloneTest {
public static void main(String[] args) throws CloneNotSupportedException {
int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9};
CloneStudent cs = new CloneStudent("ax", 19, arr);
CloneStudent css = (CloneStudent) cs.clone();
cs.getArr()[0] = 100;
System.out.println(cs.getAge() + " " + cs.getName());
cs.getCloneArr();
System.out.println();
System.out.println(css.getAge() + " " + css.getName());
css.getCloneArr();
}
}
深克隆，深拷贝：
javabean（这里的clone方法需要重写需求）
public class CloneStudent implements Cloneable {
String name;
int age;
int[] arr;
public CloneStudent(String name, int age, int[] arr) {
this.name = name;
this.age = age;
this.arr = arr;
}
public CloneStudent() {
}
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;
}
public int[] getArr() {
return arr;
}
public void setArr(int[] arr) {
this.arr = arr;
}
public void getCloneArr() {
for (int j : arr) {
System.out.print(j + " ");
}
}
@Override
protected Object clone() throws CloneNotSupportedException {
int[] a = this.arr;
int[] a1 = new int[a.length];
for (int i = 0; i < a.length; i++) {
a1[i] = a[i];
}
CloneStudent clone = (CloneStudent) super.clone();
clone.setArr(a1);
return clone;
}
}
测试类
public class CloneTest {
public static void main(String[] args) throws CloneNotSupportedException {
int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9};
CloneStudent cs = new CloneStudent("ax", 19, arr);
CloneStudent css = (CloneStudent) cs.clone();
cs.getArr()[0] = 100;
System.out.println(cs.getAge() + " " + cs.getName());
cs.getCloneArr();
System.out.println();
System.out.println(css.getAge() + " " + css.getName());
css.getCloneArr();
}
}
执行结果
原文地址：https://blog.csdn.net/2302_79847831/article/details/142435863
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