API

		String s = "abc";
        StringBuilder sb = new StringBuilder("abc");
        System.out.println(s.equals(sb));//false
        
        *String中的equals方法会先判断参数是否为字符串*
        *是字符串再比较内部属性*
        
        System.out.println(sb.equals(s));//false
        *StringBuilder仅比较地址值*
        
        (String)
        public boolean equals(Object anObject) {
            if (this == anObject) {
                return true;
            }
            return (anObject instanceof String aString)
                    && (!COMPACT_STRINGS || this.coder == aString.coder)
                    && StringLatin1.equals(value, aString.value);
    	}
        
        (StringBuilder{Object的方法})
        public boolean equals(Object obj) {
        	return (this == obj);
    	}

public static void main(String[] args) throws CloneNotSupportedException {
        Student s1 = new Student("zhangsan",18);
        Object s2 = (Student)s1.clone();
        System.out.println(s1);//@23fc625e
        System.out.println(s2);//@3f99bd52
        System.out.println(s1 == s2);//false
}

	@Override（写在JavaBean中）
    protected Object clone() throws CloneNotSupportedException {
        return super.clone();
}

	/*	1.重写Object中的clone方法
		2.让JavaBean类实现Cloneable接口
		3.创建原对象调用clone	*/

import java.util.Objects;  
public class TestDemo {  
    public static void main(String[] args) throws CloneNotSupportedException {  
       Student s1 = null;  
       var s2 = new Student("zhangsan",23);  
       boolean res = Objects.equals(s1,s2);  
       System.out.println(res);  
       //方法的底层会判断n1 ?= null，如果为null，直接返回false  
       //如果s1不为null，那么就利用s1再次调用equals方法  
       //此时s1是Student类型，所以最终还是会调用Student中的equals方法  
       //未重写->比较地址值  重写->比较属性值  
    }  
}

BigInteger bd1 = new BigInteger.valueOf(1);
BigInteger bd2 = new BigInteger.valueOf(2);
BigInteger res  = bd1.add(bd2);//产生一个新对象
//res = 3;

	//简单时间类
	Date d1 = new Date();//获取当前时间
	Date d2 = new Date(0L)//获取初始时间+0ms后的时间Thu Jan 01 08:00:00 CST 1970
	d2.getTime().sout;//0
	Date d3 = new Date(1000L)//获取初始时间+1000ms后的时间Thu Jan 01 08:00:01 CST 1970
	d3.getTime().sout;//1000

	SimpleDateFormat sdf = new  SimpleDateFormat();  
	Date  date = new Date(0L);
	String str = sdf.format(date);  
	System.out.println(str);
	
	默认格式：1970/1/1 08:00 

	SimpleDateFormat sdf = new  SimpleDateFormat("yyyy年MM月dd日 HH:mm:ss EEEE"); 
	Date  date = new Date(0L);  
	String str = sdf.format(date);  
	System.out.println(str);
	
	指定格式：1970年01月01日 08:00:00 星期四

	Calandar c = Calandar.getInstance();
	c.get(Calandar.YEAR);
	c.set(Calandar.YEAR,11)//实际为12月
	c.add(Calandar.YEAR,1)//实际为次年1月

	Integer i1 = 10;
	Integer i2 = 20;
	Integer i3 = i1 + i2;//底层：先拆箱 -> 计算 -> 再装箱赋值给i3

	int[] a =  {1,2,3,4,5,6,7,8,9,10};
	Arrays.binarySearch(arr,10);//9
	Arrays.binarySearch(arr,100)//-11

	int[] a =  {1,2,3,4,5,6,7,8,9,10};
	int[] newa = Arrays.copyOf(a);

	int[] a =  {1,2,3,4,5,6,7,8,9,10};
	int[] newa = Arrays.copyOfRange(a,0,9);
	//1 2 3 4 5 6 7 8 9

	int[] a =  {1,2,3,4,5,6,7,8,9,10};	
	Arrays.fill(a,100);//100 100 100 ...

	Arrays.sort(a);//升序

	Integer[] a =  {2,7,5,4,5,6,7,8,9,31};  
Arrays.sort(a,newComparator<Integer>() {  
	@Override  
	public int compare(Integer o1, Integer o2) {  
		return o1-o2;  
	}  
});

package MyTestDemo2;  
public class TestDemo{  
    public static void main(String[] args){  
        method(()->{  
            System.out.println("lambda:");  
            System.out.println("swimming");  
        });  
    }  
    public static void method(swim s){  
        s.swimming();  
    }  
}  
@FunctionalInterface
interface swim{  
    public void swimming();  
}

	Integer[] a =  {2,7,5,4,5,6,7,8,9,31};  
	Arrays.sort(a,(o1,o2) -> o1-o2);//升序
	Arrays.sort(a,(o1,o2) -> o2-o1);//倒序