Java语言复习

Class Inheritance & Interface Implements

• class method - static methods （Math.man(); Math.sqry()....)
• instance method - non-static methods

public static void main(String[] args) { }

Overrding vs Overloading

overriding: same name and same sigatures
overloading: same name but different signatures(parameters)

Static type vs Dynamic type

List a = new ArrayList() // Static type a = new Dynamic type ()
Dynamic method selection: java checks static type when calls method

• Compiler plays it safe and only allows us to do things according to the static type.
• For overridden methods (not overloaded methods), the actual method invoked is based
  on the dynamic type of the invoking expression (如果static type没有此方法, then compiletime error)
• Can use casting to overrule compiler type checking.

Extends

Constructors Are Not Inherited: super()

interface vs astract class

interface:

• All methods must be public.
• All variables must be public static final.
• Cannot be instantiated
• All methods are by default abstract unless specified to be default
• Can implement more than one interface per class

abstract class:

• Methods can be public or private
• Can have any types of variables
• Cannot be instantiated
• Methods are by default concrete unless specified to be abstract
• Can only implement one per class

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Lists: ordered collection of items

IntList

需要改进， 创建添加都很麻烦
为了后续 将IntList命名为 IntNode

public class IntNode{
    public int item;
    public IntNode next;

    public IntNode(int i, IntNode n){
        item= i;
        next= n;
    }
}

类LinkedList（SLList)

在list前面加一个sentinel 一个dummyhead通常会有利于对于special case, Null 的处理
大概逻辑如下：

public class SLList {
    public IntNode first;
    public int size;
    public SLList() {
        first = null;
        size = 0;
    }
    public SLList(int x) {
        first = new IntNode(x, null);
        size = 0;
    } /
    ** Adds an item to the front of the list. */
    public void addFirst(int x) {
        first = new IntNode(x, first);
        size += 1;
    }
}

Arrays

int x = new int[3];
y = new int[]{1,2,3,4};
int[] z = {1,2,3,4};
int[][] 2D = new int[4][];
arrays.length;

AList (Array based list)

resize array when size == items.length. resize(size * RFACTOR);

Java 标准list库

ArrayList

ArrayList a = new ArrayList<>();
a.add(int index, E element); // a.add(E element); add to the end of the list
a.contains();
a.size();
a.get(index);
a.remove();
a.isEmpty();
a.indexof();
a.lastIndexof();
a.toArray();
a.sort(Comparator<> c)
a.clear();
a.set(index, element); //replace
a.clone(); shallow copy

LinkedList (和上面基本一致，可以getLast/addLast）

collection list用add get / Deque用offer/peek/poll

List l = new LinkedList<>();
l.add();  // same for get 和remove: l.get(); l.getFirst(); l.getLast()
l.addFirst();
l.addLast();
l.toArray();

---

Set and Map

Set: unordered collection of strictly unique items

HashSet

Set s = new HashSet<>();
s.add();
s.contains();
s.isempty();
s.remove();

TreeSet

还没用过

Map: collection of key/value pairs

HashMap

Map map = new HashMap<>();
map.containsKey();
map.containsValue();
map.keySet();
map.value();
map.get();
map.getOrDefault();
map.put(K,V);
map.remove();
map.replace();

---

Comparable & Iterable

Comparable

import java.util.Comparator;
public class Dog implements Comparable {
    ...
    public int compareTo(Dog uddaDog) {
        return this.size - uddaDog.size;
    } 
    private static class NameComparator implements Comparator {
        public int compare(Dog a, Dog b) {
        return a.name.compareTo(b.name);
    }
} 
    public static Comparator getNameComparator() {
        return new NameComparator();
    }
}

when use: Comparator nc = Dog.getNameComparator(); retrieve the new created comparator

Iterable

如果要给class需要循环，需要 implements Iterable

public interface Iterable{
    Iterator iterator();
}

public interface Iterator{
    boolean hasNext();
    T next();
}
//举例
public class ArraySet implements Iterable{
    ...
    public Iterator iterator() {
        return new ArraySetIterator();
    }
    private class ArraySetIterator implements Iterator {
        private int wizPos;
        public ArraySetIterator() {
            wizPos = 0;
        } 
        public boolean hasNext() {
            return wizPos < size;
        } 
        public T next() {
            T returnItem = items[wizPos];
            wizPos += 1;
            return returnItem;
        }
    ...
    public static void main(String[] args) {
        ArraySet aset = new ArraySet<>();
        aset.add(5);
        aset.add(23);
        //iteration
        for (int i : aset) {
            System.out.println(i);
        }
    }
}    
    

---

StringBuilder sb = new StringBuilder("a");
sb.append("b");
sb.toString;

throw/catch exception

package