java常用方法

Posted 2020-09-29 石头-Stone

1、

byte[] b = {1,2,3,4,5,6,7};

byte[] c = new byte[5];

void System.arraycopy(b,2,c,0,c.length);

//后5个

2、

new int[1].length;

new String("1").length();

3、Object

java.lang.Object ：11

protected Object clone()throws CloneNotSupportedException

public boolean equals(Object obj)

protected void finalize()throws Throwable

public final Class<?> getClass()

public int hashCode()  

public String toString()

public final void notify()

public final void notifyAll()

public final void wait()throws InterruptedException

public final void wait(long timeout)throws InterruptedException

public final void wait(long timeout,int nanos)throws InterruptedException

：public interface Cloneable--clone()

4、String

public final class String extends Object implements Serializable, Comparable<String>, CharSequence

String(char[] value) 

String(char[] value, int offset, int count)//offset开始位置 

String(StringBuffer buffer) 

public int length()

public boolean isEmpty()

public char charAt(int index)

public void getChars(int srcBegin,int srcEnd,char[] dst,int dstBegin)

public char[] toCharArray()

public static String copyValueOf(char[] data,int offset,int count)

public int compareTo(String anotherString)  

public boolean equals(Object anObject)

public boolean equalsIgnoreCase(String anotherString)

public boolean startsWith(String prefix)

public boolean startsWith(String prefix,int toffset)

public boolean endsWith(String suffix)

public int indexOf(int ch)

public int indexOf(int ch,int fromIndex)

public int lastIndexOf(int ch)

public int indexOf(String str)

public int indexOf(String str,int fromIndex)

public int lastIndexOf(String str)

public String substring(int beginIndex)

public String substring(int beginIndex,int endIndex)

public String replace(char oldChar,char newChar)//替换所有字符

public String replaceAll(String regex,String replacement)// replaceAll("\\\\","");

public String replaceFirst(String regex,String replacement)    

public boolean matches(String regex)

public String[] split(String regex)

public String[] split(String regex,int limit)

public String toLowerCase()

public String toUpperCase()

public String trim()

public String toString()

：public interface Comparable<T>--int compareTo(T o)  

5、LinkedList

public class LinkedList<E>extends AbstractSequentialList<E>implements List<E>, Deque<E>, Cloneable, Serializable

LinkedList(Collection<? extends E> c)

：添加元素

boolean add(E e) 

void add(int index, E element)   

boolean addAll(Collection<? extends E> c)  

boolean addAll(int index, Collection<? extends E> c)  

void addFirst(E e) 

void addLast(E e) 

boolean offer(E e) //元素添加到末尾

boolean offerFirst(E e) 

boolean offerLast(E e) 

：获取元素 

E element()  //获取第一个元素

E get(int index)   

E getFirst()  

E getLast()  

E peek()  //获取第一个元素

E peekFirst()  

E peekLast() 

：移除并获取元素 

E poll() //第一个元素

E pollFirst()  

E pollLast() 

E remove()  //第一个元素

E remove(int index) 

boolean remove(Object o) 

E removeFirst()  

E removeLast() 

 

int indexOf(Object o)    

int lastIndexOf(Object o)  

E set(int index, E element)  //修改值

   

boolean contains(Object o) 

void clear() 

int size() 

Object[] toArray() 

void push(E e) //堆栈压入元素

E pop() //堆栈弹出元素

  

 

栈：

public class Stack<T> {

private LinkedList<T> storage = new LinkedList<T>();

public void push(T v){

storage.addLast(v);

}

public T peek(){

return storage.getLast();

}

public T pop(){ 

        if(!storage.isEmpty())

{

return storage.removeLast();

}     

}

public boolean empty(){

return storage.isEmpty();

}

队列：

InitQueue（）　　 ——初始化队列

EnQueue（）        ——进队列

DeQueue（）        ——出队列

IsQueueEmpty（）——判断队列是否为空

IsQueueFull（）    ——判断队列是否已满

public class Queue

{

private LinkedList storage = new LinkedList();

public void clear()//销毁队列

{

storage.clear();

}

public boolean Empty()//判断队列是否为空

{

return storage.isEmpty();

}

public int Length()//获取队列长度

{

return storage.size();

}

public void enQueue(Object o)//进队

{

storage.addFirst(o);

}

public Object deQueue()//出队

{

if(!storage.isEmpty())

{

return storage.removeLast();

}

return "队列为空";

}

public Object peekQueue()//查看队首元素

{

return storage.getLast();

}

}

6、Map

public class HashMap<K,V>extends AbstractMap<K,V>implements Map<K,V>, Cloneable, Serializable

HashMap(int initialCapacity) 

HashMap(Map<? extends K,? extends V> m) 

//增删

V put(K key, V value)  

void putAll(Map<? extends K,? extends V> m) 

V remove(Object key) 

//查询

boolean containsKey(Object key)  

boolean containsValue(Object value)

V get(Object key) 

Set<K> keySet() 

Set<Map.Entry<K,V>> entrySet()  

//其他

void clear()  

boolean isEmpty()    

int size() 

Object clone() 

7、HashSet

public class HashSet<E>extends AbstractSet<E>implements Set<E>, Cloneable, Serializable

HashSet(int initialCapacity) 

HashSet(Collection<? extends E> c) 

boolean add(E e)  

boolean remove(Object o) 

boolean contains(Object o)  

Iterator<E> iterator()  

void clear()

boolean isEmpty()

int size()   

Object clone() 

7、Collections

public class Collectionsextends Object

static <T> void copy(List<? super T> dest, List<? extends T> src) 

static boolean disjoint(Collection<?> c1, Collection<?> c2)  //两列表中有相同元素则返回true

static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) 

static <T extends Comparable<? super T>> void sort(List<T> list)  

static <T> void sort(List<T> list, Comparator<? super T> c) 

 

public interface Comparator<T>｛

int compare(T o1, T o2)；

boolean equals(Object obj)  ；  

｝

8、Arrays

public class Arraysextends Object

static <T> T[] copyOf(T[] original, int newLength)//复制一定长度  

static <T> T[] copyOfRange(T[] original, int from, int to)//复制一定范围

static boolean equals(Object[] a, Object[] a2) 

public static boolean deepEquals(Object[] a1,Object[] a2)  

static void sort(Object[] a) 

static void sort(Object[] a, int fromIndex, int toIndex) 

static <T> void sort(T[] a, Comparator<? super T> c)