Java for Life

Updates from April, 2012 Toggle Comment Threads | Keyboard Shortcuts

• 

  MohanaRao SV 7:28 pm on April 27, 2012 Permalink | Reply
  Tags: java memorymanagement   

  Memory management in java 

  Heap: is a single area where JVM allocates memory for -Objects, including method code , static variables & instance variables.

  Stack: Stack is created for each individual thread, JVM allocates memory for – local variables & arguments(reference) (values passed to method variables)

  Note : interface – all values in interface are constants i.e final static, so it’s stored on Heap only.

  When we have a declaration like this

  class Sample{ 
  int e = 1; 
  public int math (int x, int y){ 
  A a = new A(); 
  return (A.e + x + y); 
  } 
  } 
  

  Then we have:
  Stack: x, y, a
  Heap: instance a (it is A object), a.e = 1
  (Note that a in stack points out to instance a in heap)
  If instance a is no longer used, it is garbage collected

   

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• 

  MohanaRao SV 3:22 pm on March 18, 2012 Permalink | Reply
  Tags: Java   

  Method to count number of repeated special characters in a given String. 

  
  public Map<Character, Integer> charIntMap(String str) {
  		Map<Character, Integer> map = new HashMap<Character, Integer>();
  		char[] charString = str.toCharArray();
  		int count = 1;
  		for (int i = 0; i < (charString.length - 1); i++) {
  			if (!Character.isLetter(charString[i])) {
  				if (!map.containsKey(charString[i])) {
  					map.put(charString[i], count);
  				} else {
  					map.put(charString[i], count++);
  				}
  			}
  		}
  		return map;
  	}
  
  
   
• 

  MohanaRao SV 1:02 am on March 12, 2012 Permalink | Reply
  Tags: core java.   

  Example for overriding Hashcode and Equals methods. 

  Whenever you are working with the collections HashMap, HashSet then you have to override pojo hashcode and equals method.

  
  package com.stackoverflow.java.core;
  
  import java.util.HashMap;
  import java.util.Map;
  
  public class Employee {
  	private String name;
  	private String sex;
  	private int salary;
  	private int age;
  
  	public String getName() {
  		return name;
  	}
  
  	public void setName(String name) {
  		this.name = name;
  	}
  
  	public String getSex() {
  		return sex;
  	}
  
  	public void setSex(String sex) {
  		this.sex = sex;
  	}
  
  	public int getSalary() {
  		return salary;
  	}
  
  	public void setSalary(int salary) {
  		this.salary = salary;
  	}
  
  	public int getAge() {
  		return age;
  	}
  
  	public void setAge(int age) {
  		this.age = age;
  	}
  
  	@Override
  	public int hashCode() {
                    //Not taken care when genrating hashcode.
  		int hashcode = this.age * 2 + this.salary * 2;
  		return hashcode;
  	}
  
  	@Override
  	public boolean equals(Object obj) {
  		if (this == obj)
  			return true;
  		if (obj == null)
  			return false;
  		if (getClass() != this.getClass())
  			return false;
  		Employee employee = (Employee) (obj);
  		if ((this.name.equals(employee.name) && (this.sex.equals(employee.sex)
  				&& (this.age == employee.age) && (this.salary == employee.salary)))) {
  			return true;
  		} else {
  			return false;
  		}
  	}