变量 - Variable

• byte
• short
• int
• long

• float
  float的精确度比double低
  Float.MIN_VALUE并不是最小的浮点数
• double
  数据类型转换
  小的数据类型会默认转成大的数据类型
  大的数据类型需强制转成小的数据类型
• boolean
  &&
  ||
  ！
  lazy evaluation
• char
  ASCII 码
  Unicode
  可用(int)(char c)转换一个char到int，转为对应的ASCII值
  有+，-运算
• reference
  copy value
  • 练习1

package com.company;

class MyInteger{
    public int num;
    public MyInteger(int num){
        this.num = num;
    }
}

public class Main {

    public static void func1(int a,int b) {
        int t = a;
        a = b;
        b = t;
    }
    public static void func2(Integer a,Integer b){
        Integer t = a;
        a = b;
        b = t;
    }

    public static void func3(MyInteger a,MyInteger b){
        int t = a.num;
        a.num = b.num;
        b.num = t;
    }

    public static void main(String[] args) {
        int a1 = 2, b1 = 3;
        func1(a1,b1);
        Integer a2 = 2, b2 = 3;
        func2(a2,b2);
        MyInteger a3 = new MyInteger(2), b3 = new MyInteger(3);
        func3(a3,b3);
        System.out.print(a1 + " " + b1 + " ");
        System.out.print(a2 + " " + b2 + " ");
        System.out.print(a3.num + " " +b3.num);
    }
}

其输出结果为

2 3 2 3 3 2

• 练习2

String s1 = "abc";
String s2 = "abc";
System.out.println(s1 == s2);
System.out.println(s2.equals(s2));
String s3 = new String("def");
String s4 = new String("def");
System.out.println(s3 == s4);
System.out.println(s3.equals(s4));

其输出结果为

true
true
false
true

• Lintcode 相关题目
  Reference
  Hex Conversion
  Reverse 3-digit Integer