3分钟快速阅读-《Effective Java》(一)

// 工厂实例类代码
public class FactoryDemo {

    private final Long ID;
    private final String adress;

    private final int age;
    private final String name;

    public static class Builder {
        private final int age;
        private final String name;

        private Long ID = 0L;
        private String adress = "";

        public Builder(int age, String name) {
            this.age = age;
            this.name = name;
        }

        public Builder ID(Long ID){
            this.ID = ID;
            return this;
        }

        public Builder adress(String adress){
            this.adress = adress;
            return this;
        }

        public FactoryDemo build(){
            return new FactoryDemo(this);
        }
    }

    private FactoryDemo(Builder builder){
        this.ID = builder.ID;
        this.adress = builder.adress;
        this.age = builder.age;
        this.name = builder.name;
    }
}

// 客户端调用代码
FactoryDemo build = new FactoryDemo.Builder(18, "大爷").ID(35062819920914L).adress("福建漳州").build();

//方式1
public class Elvis {
    public static fianl Elvis INSTANCE = new Elvis();
    private Elvis(){}
}

//方式2
public class Elvis {
    public static fianl Elvis INSTANCE = new Elvis();
    private Elvis(){}
    public static Elvis getInstance(){
        return INSTANCE;
    }
}

public enum Elvis {
    INSTANCE;
    //业务逻辑方法
    public void run(){
        System.out.println("处理业务逻辑");
    }
}

public class Test {

    public static void main(String[] args) {

        Long sum = 0L;
        long begin = System.currentTimeMillis();
        for(int i = 0 ;i<=100000;i++){
            sum += 1;
        }
        long end = System.currentTimeMillis();
        System.out.println("Long总耗时:"+(end-begin));//5ms

        long sum1 = 0L;
        long begin1 = System.currentTimeMillis();
        for(int i = 0 ;i<=100000;i++){
            sum1 += 1;
        }
        long end1 = System.currentTimeMillis();
        System.out.println("long总耗时:"+(end1-begin1));//0ms

    }
}

public class Test {

    public static void main(String[] args) {
        long begin = System.currentTimeMillis();
        for(int i = 0 ;i<=10000;i++){
            String str = new String("sb");
        }
        long end = System.currentTimeMillis();
        System.out.println("new总耗时:"+(end - begin));//2ms

        long begin1 = System.currentTimeMillis();
        for(int i = 0 ;i<=10000;i++){
            String str = "sb";
        }
        long end1 = System.currentTimeMillis();
        System.out.println("非new总耗时:"+(end1 - begin1));//0ms
    }
}

//以下这段代码主要问题在于pop出栈的对象,还对原有的对象在内存中的地址/存在着引用,所以需要对已经出栈的对象做空引用的处理
public class StackDemo {
    private Object[] elements;
    private int size = 0;
    private final int DEFAULT_INITIAL_CAPACITY = 16;

    /**
     * 功能描述: 
     * 〈初始化栈〉
     *
     * @params : []
     * @return : 
     * @author : cwl
     * @date : 2019/5/5 16:59
     */
    public StackDemo(){
        elements = new Object[DEFAULT_INITIAL_CAPACITY];
    }
    
    /**
     * 功能描述: 
     * 〈压栈〉
     *
     * @params : [o]
     * @return : void
     * @author : cwl
     * @date : 2019/5/5 16:58
     */
    public void push(Object o){
        ensureCapacity();
        elements[size++] = o;
    }
    
    /**
     * 功能描述: 
     * 〈出栈〉
     *
     * @params : []
     * @return : java.lang.Object
     * @author : cwl
     * @date : 2019/5/5 16:59
     */
    public Object pop(){
        if (size == 0){
            throw new EmptyStackException();
        }
        return elements[size--];
    }
    
    /**
     * 功能描述: 
     * 〈自动扩容〉
     *
     * @params : []
     * @return : void
     * @author : cwl
     * @date : 2019/5/5 16:59
     */
    private void ensureCapacity() {
        if(elements.length == size){
            elements = Arrays.copyOf(elements,2*size+1);
        }
    }
}

 public Object pop(){
        if (size == 0){
            throw new EmptyStackException();
        }
        elements[size] =null;//将出栈的元素设置为空引用
        return elements[size--];
 }

public class PhoneNumber {
    private final short areaCode;
    private final short prefix;
    private final String lineNumber;

    public PhoneNumber(int areaCode, int prefix, String lineNumber) {
        rangeCheck(areaCode,999,"areaCode");
        this.areaCode = (short) areaCode;
        this.prefix = (short) prefix;
        this.lineNumber = lineNumber;
    }

    private void rangeCheck(int arg, int max, String name) {
        if(arg < 0 || arg > max){
            throw new IllegalArgumentException(name + ":" +arg);
        }
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (!(o instanceof PhoneNumber)) return false;
        PhoneNumber that = (PhoneNumber) o;
        return areaCode == that.areaCode &&
                prefix == that.prefix &&
                lineNumber.equals(that.lineNumber);
    }
}

Map<PhoneNumber,String> numberStringMap = new HashMap<>();
        numberStringMap.put(new PhoneNumber(180,286,"6849"),"Jenny");

//代码示例1:
    @Override
    public int hashCode() {
        return Objects.hash(areaCode, prefix, lineNumber);
    }